@article{paret_rodriguez_mayorga_velotti_lodree_2023, title={Agent-Based Simulation of Spontaneous Volunteer Convergence to Improve Disaster Planning}, volume={24}, ISSN={["1527-6996"]}, url={https://doi.org/10.1061/NHREFO.NHENG-1659}, DOI={10.1061/NHREFO.NHENG-1659}, abstractNote={The involvement of spontaneous volunteers (SVs) in disaster response represents a significant resource. However, existing emergency management plans often fail to take spontaneous volunteers into account due to negative perceptions and uncertainty about SV convergence. We developed an agent-based simulation model of spontaneous volunteer convergence to aid the disaster response planning process. The model considers a heterogeneous population of agents, each with unique attributes such as motivation, opinion, and site choice behavior. Model development was informed by the literature as well as interviews with volunteers and volunteer managers, participant observations, and discussions with practitioners. To illustrate the practical value of the model, we present a case study that addressed research questions related to volunteer reception centers and volunteer assignment policies. This transdisciplinary study bridges the gap between operations research and management science and social science, and provides a new decision aid to help improve the integration of spontaneous volunteers in disaster management plans.}, number={2}, journal={NATURAL HAZARDS REVIEW}, author={Paret, Kyle and Rodriguez, Sebastian A. and Mayorga, Maria E. and Velotti, Lucia and Lodree, Emmett J.}, year={2023}, month={May} }
 @article{li_tobey_mayorga_caltagirone_ozaltin_2023, title={Detecting Human Trafficking: Automated Classification of Online Customer Reviews of Massage Businesses}, volume={2}, ISSN={["1526-5498"]}, DOI={10.1287/msom.2023.1196}, abstractNote={Problem definition: Approximately 11,000 alleged illicit massage businesses (IMBs) exist across the United States hidden in plain sight among legitimate businesses. These illicit businesses frequently exploit workers, many of whom are victims of human trafficking, forced or coerced to provide commercial sex. Academic/practical relevance: Although IMB review boards like Rubmaps.ch can provide first-hand information to identify IMBs, these sites are likely to be closed by law enforcement. Open websites like Yelp.com provide more accessible and detailed information about a larger set of massage businesses. Reviews from these sites can be screened for risk factors of trafficking. Methodology: We develop a natural language processing approach to detect online customer reviews that indicate a massage business is likely engaged in human trafficking. We label data sets of Yelp reviews using knowledge of known IMBs. We develop a lexicon of key words/phrases related to human trafficking and commercial sex acts. We then build two classification models based on this lexicon. We also train two classification models using embeddings from the bidirectional encoder representations from transformers (BERT) model and the Doc2Vec model. Results: We evaluate the performance of these classification models and various ensemble models. The lexicon-based models achieve high precision, whereas the embedding-based models have relatively high recall. The ensemble models provide a compromise and achieve the best performance on the out-of-sample test. Our results verify the usefulness of ensemble methods for building robust models to detect risk factors of human trafficking in reviews on open websites like Yelp. Managerial implications: The proposed models can save countless hours in IMB investigations by automatically sorting through large quantities of data to flag potential illicit activity, eliminating the need for manual screening of these reviews by law enforcement and other stakeholders. Funding: This work was supported by the National Science Foundation [Grant 1936331]. Supplemental Material: The online appendix is available at https://doi.org/10.1287/msom.2023.1196 .}, journal={M&SOM-MANUFACTURING & SERVICE OPERATIONS MANAGEMENT}, author={Li, Ruoting and Tobey, Margaret and Mayorga, Maria E. and Caltagirone, Sherrie and Ozaltin, Osman Y.}, year={2023}, month={Feb} }
 @article{hicklin_meghan c. o'leary_nambiar_mayorga_wheeler_davis_richardson_tangka_lich_2022, title={Assessing the impact of multicomponent interventions on colorectal cancer screening through simulation: What would it take to reach national screening targets in North Carolina}, volume={162}, ISSN={["1096-0260"]}, DOI={10.1016/j.ypmed.2022.107126}, abstractNote={Healthy People 2020 and the National Colorectal Cancer Roundtable established colorectal cancer (CRC) screening targets of 70.5% and 80%, respectively. While evidence-based interventions (EBIs) have increased CRC screening, the ability to achieve these targets at the population level remains uncertain. We simulated the impact of multicomponent interventions in North Carolina over 5 years to assess the potential for meeting national screening targets. Each intervention scenario is described as a core EBI with additional components indicated by the "+" symbol: patient navigation for screening colonoscopy (PN-for-Col+), mailed fecal immunochemical testing (MailedFIT+), MailedFIT+ targeted to Medicaid enrollees (MailedFIT + forMd), and provider assessment and feedback (PAF+). Each intervention was simulated with and without Medicaid expansion and at different levels of exposure (i.e., reach) for targeted populations. Outcomes included the percent up-to-date overall and by sociodemographic subgroups and number of CRC cases and deaths averted. Each multicomponent intervention was associated with increased CRC screening and averted both CRC cases and deaths; three had the potential to reach screening targets. PN-for-Col + achieved the 70.5% target with 97% reach after 1 year, and the 80% target with 78% reach after 5 years. MailedFIT+ achieved the 70.5% target with 74% reach after 1 year and 5 years. In the Medicaid population, assuming Medicaid expansion, MailedFIT + forMd reached the 70.5% target after 5 years with 97% reach. This study clarifies the potential for states to reach national CRC screening targets using multicomponent EBIs, but decision-makers also should consider tradeoffs in cost, reach, and ability to reduce disparities when selecting interventions.}, journal={PREVENTIVE MEDICINE}, author={Hicklin, Karen and Meghan C. O'Leary and Nambiar, Siddhartha and Mayorga, Maria E. and Wheeler, Stephanie B. and Davis, Melinda M. and Richardson, Lisa C. and Tangka, Florence K. L. and Lich, Kristen Hassmiller}, year={2022}, month={Sep} }
 @article{biddell_johnson_patel_smith_hecht_swann_mayorga_lich_2022, title={Cross-sector decision landscape in response to COVID-19: A qualitative network mapping analysis of North Carolina decision-makers}, volume={10}, ISSN={["2296-2565"]}, DOI={10.3389/fpubh.2022.906602}, abstractNote={Introduction The COVID-19 pandemic response has demonstrated the interconnectedness of individuals, organizations, and other entities jointly contributing to the production of community health. This response has involved stakeholders from numerous sectors who have been faced with new decisions, objectives, and constraints. We examined the cross-sector organizational decision landscape that formed in response to the COVID-19 pandemic in North Carolina. Methods We conducted virtual semi-structured interviews with 44 organizational decision-makers representing nine sectors in North Carolina between October 2020 and January 2021 to understand the decision-making landscape within the first year of the COVID-19 pandemic. In line with a complexity/systems thinking lens, we defined the decision landscape as including decision-maker roles, key decisions, and interrelationships involved in producing community health. We used network mapping and conventional content analysis to analyze transcribed interviews, identifying relationships between stakeholders and synthesizing key themes. Results Decision-maker roles were characterized by underlying tensions between balancing organizational mission with employee/community health and navigating organizational vs. individual responsibility for reducing transmission. Decision-makers' roles informed their perspectives and goals, which influenced decision outcomes. Key decisions fell into several broad categories, including how to translate public health guidance into practice; when to institute, and subsequently loosen, public health restrictions; and how to address downstream social and economic impacts of public health restrictions. Lastly, given limited and changing information, as well as limited resources and expertise, the COVID-19 response required cross-sector collaboration, which was commonly coordinated by local health departments who had the most connections of all organization types in the resulting network map. Conclusions By documenting the local, cross-sector decision landscape that formed in response to COVID-19, we illuminate the impacts different organizations may have on information/misinformation, prevention behaviors, and, ultimately, health. Public health researchers and practitioners must understand, and work within, this complex decision landscape when responding to COVID-19 and future community health challenges.}, journal={FRONTIERS IN PUBLIC HEALTH}, author={Biddell, Caitlin B. B. and Johnson, Karl T. T. and Patel, Mehul D. D. and Smith, Raymond L. L. and Hecht, Hillary K. K. and Swann, Julie L. L. and Mayorga, Maria E. E. and Lich, Kristen Hassmiller}, year={2022}, month={Aug} }
 @article{shi_mayorga_su_li_martin_zhang_2022, title={GENERATION 1.5: YEARS IN THE UNITED STATES AND OTHER FACTORS AFFECTING SMOKING BEHAVIORS AMONG ASIAN AMERICANS}, volume={32}, ISSN={["1945-0826"]}, DOI={10.18865/ed.32.2.75}, abstractNote={Introduction: Generation 1.5, immigrants who moved to a different country before adulthood, are hypothesized to have unique cognitive and behavioral patterns. We ex­amined the possible differences in cigarette smoking between Asian subpopulations who arrived in the United States at different life stages.Methods: Using the Asian subsample of the 2015 Tobacco Use Supplement to the Cur­rent Population Survey, we tested this Gen­eration 1.5 hypothesis with their smoking behavior. This dataset was chosen because its large sample size allowed for a national-level analysis of the Asian subsamples by sex, while other national datasets might not have adequate sample sizes for analysis of these subpopulations. The outcome variable was defined as whether the survey respondent had ever smoked 100 cigarettes or more, with the key independent variable operationalized as whether the respon­dent was: 1) born in the United States; 2) entered the United States before 12; 3) entered between 12 and 19; and 4) entered after 19. Logistic regressions were run to examine the associations with covariates including the respondent’s age, educational attainment, and household income.Results: Asian men who entered before 12 were less likely to have ever smoked 100 cigarettes than those who immigrated after 19; for Asian women, three groups (born in the United States, entered before 12, en­tered between 12 and 19) were more likely to have smoked 100 cigarettes than those who immigrated after 19.Conclusions: While Asian men who came to the United States before 12 were less at risk for cigarette smoking than those who immigrated in adulthood, the pattern was the opposite among Asian women. Those who spent their childhood in the United States were more likely to smoke than those who came to the United States in adult­hood. These patterns might result from the cultural differences between US and Asian countries, and bear policy relevance for the tobacco control efforts among Asian Americans. Ethn Dis. 2022;32(2):75-80; doi:10.18865/ed.32.2.75}, number={2}, journal={ETHNICITY & DISEASE}, author={Shi, Lu and Mayorga, Maria and Su, Dejun and Li, Yan and Martin, Emily and Zhang, Donglan}, year={2022}, pages={75–80} }
 @article{tobey_li_ozaltin_mayorga_caltagirone_2022, title={Interpretable models for the automated detection of human trafficking in illicit massage businesses}, volume={8}, ISSN={["2472-5862"]}, DOI={10.1080/24725854.2022.2113187}, abstractNote={Sexually oriented establishments across the United States often pose as massage businesses and force victim workers into a hybrid of sex and labor trafficking, simultaneously harming the legitimate massage industry. Stakeholders with varied goals and approaches to dismantling the illicit massage industry all report the need for multi-source data to clearly and transparently identify the worst offenders and highlight patterns in behaviors. We utilize findings from primary stakeholder interviews with law enforcement, regulatory bodies, legitimate massage practitioners, and subject-matter experts from nonprofit organizations to identify data sources and potential indicators of illicit massage businesses (IMBs). We focus our analysis on data from open sources in Texas and Florida including customer reviews and business data from Yelp.com, the U.S. Census, and GIS files such as truck stop, highway, and military base locations. We build two interpretable prediction models, risk scores and optimal decision trees, to determine the risk that a given massage establishment is an IMB. The proposed multi-source data-based approach and interpretable models can be used by stakeholders at all levels to save time and resources, serve victim-workers, and support well informed regulatory efforts.}, journal={IISE TRANSACTIONS}, author={Tobey, Margaret and Li, Ruoting and Ozaltin, Osman Y. and Mayorga, Maria E. and Caltagirone, Sherrie}, year={2022}, month={Aug} }
 @article{zhang_mayorga_ivy_lich_swann_2022, title={Modeling the Impact of Nonpharmaceutical Interventions on COVID-19 Transmission in K-12 Schools}, volume={7}, ISSN={["2381-4683"]}, url={https://doi.org/10.1177/23814683221140866}, DOI={10.1177/23814683221140866}, abstractNote={Background. The novel coronavirus SARS-CoV-2 spread across the world causing many waves of COVID-19. Children were at high risk of being exposed to the disease because they were not eligible for vaccination during the first 20 mo of the pandemic in the United States. While children 5 y and older are now eligible to receive a COVID-19 vaccine in the United States, vaccination rates remain low despite most schools returning to in-person instruction. Nonpharmaceutical interventions (NPIs) are important for controlling the spread of COVID-19 in K-12 schools. US school districts used varied and layered mitigation strategies during the pandemic. The goal of this article is to analyze the impact of different NPIs on COVID-19 transmission within K-12 schools. Methods. We developed a deterministic stratified SEIR model that captures the role of social contacts between cohorts in disease transmission to estimate COVID-19 incidence under different NPIs including masks, random screening, contact reduction, school closures, and test-to-stay. We designed contact matrices to simulate the contact patterns between students and teachers within schools. We estimated the proportion of susceptible infected associated with each intervention over 1 semester under the Omicron variant. Results. We find that masks and reducing contacts can greatly reduce new infections among students. Weekly screening tests also have a positive impact on disease mitigation. While self-quarantining symptomatic infections and school closures are effective measures for decreasing semester-end infections, they increase absenteeism. Conclusion. The model provides a useful tool for evaluating the impact of a variety of NPIs on disease transmission in K-12 schools. While the model is tested under Omicron variant parameters in US K-12 schools, it can be adapted to study other populations under different disease settings. Highlights A stratified SEIR model was developed that captures the role of social contacts in K-12 schools to estimate COVID-19 transmission under different nonpharmaceutical interventions. While masks, random screening, contact reduction, school closures, and test-to-stay are all beneficial interventions, masks and contact reduction resulted in the greatest reduction in new infections among students from the tested scenarios. Layered interventions provide more benefits than implementing interventions independently.}, number={2}, journal={MDM POLICY & PRACTICE}, author={Zhang, Yiwei and Mayorga, Maria E. and Ivy, Julie and Lich, Kristen Hassmiller and Swann, Julie L.}, year={2022} }
 @article{johnson_biddell_hecht_lich_swann_delamater_mayorga_ivy_smith_patel_2022, title={Organizational decision-making during COVID-19: A qualitative analysis of the organizational decision-making system in the United States during COVID-19}, volume={11}, ISSN={["1468-5973"]}, DOI={10.1111/1468-5973.12437}, abstractNote={This study sought to understand COVID-19-related organizational decisions were made across sectors. To gain this understanding, we conducted semi-structured interviews with organizational decision-makers in North Carolina about their experiences responding to COVID-19. Conventional content analysis was used to analyse the context, inputs, and processes involved in decision-making. Between October 2020 and February 2021, we interviewed 44 decision-makers from the following sectors: business (n = 4), community non-profit (n = 3), county government (n = 4), healthcare (n = 5), local public health (n = 5), public safety (n = 7), religious (n = 6), education (n = 7) and transportation (n = 3). We found that during the pandemic, organizations looked to scientific authorities, the decisions of peer organizations, data about COVID-19, and their own experience with prior crises. Interpretation of inputs was informed by current political events, societal trends, and organization mission. Decision-makers had to account for divergent internal opinions and community behaviour. To navigate inputs and contextual factors, organizations decentralized decision-making authority, formed auxiliary decision-making bodies, learned to resolve internal conflicts, learned in real time from their crisis response, and routinely communicated decisions with their communities. In conclusion, aligned with systems and contingency theories of decision-making, decision-making during COVID-19 depended on an organization's ‘fit’ within the specifics of their existing system and their ability to orient the dynamics of that system to their own goals.}, journal={JOURNAL OF CONTINGENCIES AND CRISIS MANAGEMENT}, author={Johnson, Karl and Biddell, Caitlin B. B. and Hecht, Hillary K. K. and Lich, Kristen H. H. and Swann, Julie and Delamater, Paul and Mayorga, Maria and Ivy, Julie and Smith, Raymond L. L. and Patel, Mehul D. D.}, year={2022}, month={Nov} }
 @article{swan_mayorga_ivy_2022, title={The SMART Framework: Selection of Machine Learning Algorithms With ReplicaTions-A Case Study on the Microvascular Complications of Diabetes}, volume={26}, ISSN={["2168-2208"]}, DOI={10.1109/JBHI.2021.3094777}, abstractNote={Over 34 million people in the US have diabetes, a major cause of blindness, renal failure, and amputations. Machine learning (ML) models can predict high-risk patients to help prevent adverse outcomes. Selecting the 'best' prediction model for a given disease, population, and clinical application is challenging due to the hundreds of health-related ML models in the literature and the increasing availability of ML methodologies. To support this decision process, we developed the Selection of Machine-learning Algorithms with ReplicaTions (SMART) Framework that integrates building and selecting ML models with decision theory. We build ML models and estimate performance for multiple plausible future populations with a replicated nested cross-validation technique. We rank ML models by simulating decision-maker priorities, using a range of accuracy measures (e.g., AUC) and robustness metrics from decision theory (e.g., minimax Regret). We present the SMART Framework through a case study on the microvascular complications of diabetes using data from the ACCORD clinical trial. We compare selections made by risk-averse, -neutral, and -seeking decision-makers, finding agreement in 80% of the risk-averse and risk-neutral selections, with the risk-averse selections showing consistency for a given complication. We also found that the models that best predicted outcomes in the validation set were those with low performance variance on the testing set, indicating a risk-averse approach in model selection is ideal when there is a potential for high population feature variability. The SMART Framework is a powerful, interactive tool that incorporates various ML algorithms and stakeholder preferences, generalizable to new data and technological advancements.}, number={2}, journal={IEEE JOURNAL OF BIOMEDICAL AND HEALTH INFORMATICS}, author={Swan, Breanna P. and Mayorga, Maria E. and Ivy, Julie S.}, year={2022}, month={Feb}, pages={809–817} }
 @article{townsley_koutouan_mayorga_mills_davis_hasmiller lich_2022, title={When History and Heterogeneity Matter: A Tutorial on the Impact of Markov Model Specifications in the Context of Colorectal Cancer Screening}, volume={5}, ISSN={["1552-681X"]}, DOI={10.1177/0272989X221097386}, abstractNote={Markov models are used in health research to simulate health care utilization and disease states over time. Health phenomena, however, are complex, and the memoryless assumption of Markov models may not appropriately represent reality. This tutorial provides guidance on the use of Markov models of different orders and stratification levels in health decision-analytic modeling. Colorectal cancer (CRC) screening is used as a case example to examine the impact of using different Markov modeling approaches on CRC outcomes.This study used insurance claims data from commercially insured individuals in Oregon to estimate transition probabilities between CRC screening states (no screen, colonoscopy, fecal immunochemical test or fecal occult blood test). First-order, first-order stratified by sex and geography, and third-order Markov models were compared. Screening trajectories produced from the different Markov models were incorporated into a microsimulation model that simulated the natural history of CRC disease progression. Simulation outcomes (e.g., future screening choices, CRC incidence, deaths due to CRC) were compared across models.Simulated CRC screening trajectories and resulting CRC outcomes varied depending on the Markov modeling approach used. For example, when using the first-order, first-order stratified, and third-order Markov models, 30%, 31%, and 44% of individuals used colonoscopy as their only screening modality, respectively. Screening trajectories based on the third-order Markov model predicted that a higher percentage of individuals were up-to-date with CRC screening as compared with the other Markov models.The study was limited to insurance claims data spanning 5 y. It was not possible to validate which Markov model better predicts long-term screening behavior and outcomes.Findings demonstrate the impact that different order and stratification assumptions can have in decision-analytic models.This tutorial uses colorectal cancer screening as a case example to provide guidance on the use of Markov models of different orders and stratification levels in health decision-analytic models.Colorectal cancer screening trajectories and projected health outcomes were sensitive to the use of alternate Markov model specifications.Although data limitations precluded the assessment of model accuracy beyond a 5-y period, within the 5-y period, the third-order Markov model was slightly more accurate in predicting the fifth colorectal cancer screening action than the first-order Markov model.Findings from this tutorial demonstrate the importance of examining the memoryless assumption of the first-order Markov model when simulating health care utilization over time.}, journal={MEDICAL DECISION MAKING}, author={Townsley, Rachel M. and Koutouan, Priscille R. and Mayorga, Maria E. and Mills, Sarah D. and Davis, Melinda M. and Hasmiller Lich, Kristen}, year={2022}, month={May} }
 @article{paret_mayorga_lodree_2021, title={Assigning spontaneous volunteers to relief efforts under uncertainty in task demand and volunteer availability}, volume={99}, ISSN={["1873-5274"]}, DOI={10.1016/j.omega.2020.102228}, abstractNote={Abstract In the wake of a disaster, people from nearby areas often converge to assist the affected community. Spontaneous volunteers are not affiliated with relief agencies but are in a unique position to provide invaluable aid at a crucial point in the disaster cycle. Often, these volunteers are ineffectively used or refused altogether. Volunteer Reception Centers (VRCs) can benefit from improved strategies to integrate the influx of spontaneous volunteers. In this paper, a multi-server queuing model is formulated to represent the dynamics of assigning spontaneous volunteers to tasks in a post-disaster setting. In particular, we consider the case of stochastic arrival of demand for service and stochastic arrival of volunteers, whose time in service is also stochastic. These assumptions mimic disaster relief tasks such as distribution of relief items, where both beneficiaries and volunteers arrive randomly. An optimal policy for assigning volunteers to tasks is generated using a Markov Decision Process. We then use simulation to compare the optimal policy against several heuristic policies and discuss real world implications.}, journal={OMEGA-INTERNATIONAL JOURNAL OF MANAGEMENT SCIENCE}, author={Paret, Kyle E. and Mayorga, Maria E. and Lodree, Emmett J.}, year={2021}, month={Mar} }
 @article{patel_rosenstrom_ivy_mayorga_keskinocak_boyce_hassmiller lich_smith_johnson_delamater_et al._2021, title={Association of Simulated COVID-19 Vaccination and Nonpharmaceutical Interventions With Infections, Hospitalizations, and Mortality}, volume={4}, ISSN={["2574-3805"]}, DOI={10.1001/jamanetworkopen.2021.10782}, abstractNote={Vaccination against SARS-CoV-2 has the potential to significantly reduce transmission and COVID-19 morbidity and mortality. The relative importance of vaccination strategies and nonpharmaceutical interventions (NPIs) is not well understood.To assess the association of simulated COVID-19 vaccine efficacy and coverage scenarios with and without NPIs with infections, hospitalizations, and deaths.An established agent-based decision analytical model was used to simulate COVID-19 transmission and progression from March 24, 2020, to September 23, 2021. The model simulated COVID-19 spread in North Carolina, a US state of 10.5 million people. A network of 1 017 720 agents was constructed from US Census data to represent the statewide population.Scenarios of vaccine efficacy (50% and 90%), vaccine coverage (25%, 50%, and 75% at the end of a 6-month distribution period), and NPIs (reduced mobility, school closings, and use of face masks) maintained and removed during vaccine distribution.Risks of infection from the start of vaccine distribution and risk differences comparing scenarios. Outcome means and SDs were calculated across replications.In the worst-case vaccination scenario (50% efficacy, 25% coverage), a mean (SD) of 2 231 134 (117 867) new infections occurred after vaccination began with NPIs removed, and a mean (SD) of 799 949 (60 279) new infections occurred with NPIs maintained during 11 months. In contrast, in the best-case scenario (90% efficacy, 75% coverage), a mean (SD) of 527 409 (40 637) new infections occurred with NPIs removed and a mean (SD) of 450 575 (32 716) new infections occurred with NPIs maintained. With NPIs removed, lower efficacy (50%) and higher coverage (75%) reduced infection risk by a greater magnitude than higher efficacy (90%) and lower coverage (25%) compared with the worst-case scenario (mean [SD] absolute risk reduction, 13% [1%] and 8% [1%], respectively).Simulation outcomes suggest that removing NPIs while vaccines are distributed may result in substantial increases in infections, hospitalizations, and deaths. Furthermore, as NPIs are removed, higher vaccination coverage with less efficacious vaccines can contribute to a larger reduction in risk of SARS-CoV-2 infection compared with more efficacious vaccines at lower coverage. These findings highlight the need for well-resourced and coordinated efforts to achieve high vaccine coverage and continued adherence to NPIs before many prepandemic activities can be resumed.}, number={6}, journal={JAMA NETWORK OPEN}, author={Patel, Mehul D. and Rosenstrom, Erik and Ivy, Julie S. and Mayorga, Maria E. and Keskinocak, Pinar and Boyce, Ross M. and Hassmiller Lich, Kristen and Smith, Raymond L., III and Johnson, Karl T. and Delamater, Paul L. and et al.}, year={2021}, month={Jun} }
 @article{ju_kim_ausin_mayorga_chi_2021, title={To Reduce Healthcare Workload: Identify Critical Sepsis Progression Moments through Deep Reinforcement Learning}, ISSN={["2639-1589"]}, DOI={10.1109/BigData52589.2021.9671407}, abstractNote={Healthcare systems are struggling with increasing workloads that adversely affect quality of care and patient outcomes. When clinical practitioners have to make countless medical decisions, they may not always able to make them consistently or spend time on them. In this work, we formulate clinical decision making as a reinforcement learning (RL) problem and propose a human-controlled machine-assisted (HC-MA) decision making framework whereby we can simultaneously give clinical practitioners (the humans) control over the decision-making process while supporting effective decision-making. In our HC-MA framework, the role of the RL agent is to nudge clinicians only if they make suboptimal decisions at critical moments. This framework is supported by a general Critical Deep RL (Critical-DRL) approach, which uses Long-Short Term Rewards (LSTRs) and Critical Deep Q-learning Networks (CriQNs). Critical-DRL’s effectiveness has been evaluated in both a GridWorld game and real-world datasets from two medical systems: a large health system in the northeast of USA, referred as NEMed and Mayo Clinic in Rochester, Minnesota, USA for septic patient treatment. We found that our Critical-DRL approach, by which decisions are made at critical junctures, is as effective as a fully executed DRL policy and moreover, it enables us to identify the critical moments in the septic treatment process, thus greatly reducing burden on medical decision-makers by allowing them to make critical clinical decisions without negatively impacting outcomes.}, journal={2021 IEEE INTERNATIONAL CONFERENCE ON BIG DATA (BIG DATA)}, author={Ju, Song and Kim, Yeo Jin and Ausin, Markel Sanz and Mayorga, Maria E. and Chi, Min}, year={2021}, pages={1640–1646} }
 @article{swan_nambiar_koutouan_mayorga_ivy_fransen_2020, title={EVALUATING DIABETIC RETINOPATHY SCREENING INTERVENTIONS IN A MICROSIMULATION MODEL}, ISSN={["0891-7736"]}, DOI={10.1109/WSC48552.2020.9384074}, abstractNote={Diabetic retinopathy (DR) is the leading cause of blindness for working age Americans. Early detection, timely treatment, and appropriate follow-up care reduce the risk of severe vision loss from DR by 95%, yet, less than 50% of people with diabetes adhere to the recommended screening guidelines. Diabetes is a complicated disease for patients and their physicians to manage. We developed a microsimulation integrating the natural history model of DR with a patient’s interaction with the care system. We introduced a DR screening device in primary care, with and without care coordination by a medical professional, in two interventions to the current care path. We found the interventions increased adherence of patients with vision-threatening DR (VTDR) to follow-up eye care, decreased the number of ‘unnecessary’ visits in specialty eye care from patients without VTDR, and decreased the total years spent blind.}, journal={2020 WINTER SIMULATION CONFERENCE (WSC)}, author={Swan, Breanna and Nambiar, Siddhartha and Koutouan, Priscille and Mayorga, Maria E. and Ivy, Julie and Fransen, Stephen}, year={2020}, pages={944–955} }
 @misc{mckenzie_mayorga_miller_singh_arnold_romero-brufau_2020, title={Notice to comply: A systematic review of clinician compliance with guidelines surrounding acute hospital-based infection management}, volume={48}, ISSN={["1527-3296"]}, DOI={10.1016/j.ajic.2020.02.006}, abstractNote={•Guideline design and implementation vary in studies reporting clinician compliance. •We systematically reviewed articles reporting compliance with infection guidelines. •We characterized compliance results and compared intervention strategies for trends. •Multimodal interventions seem to produce the greatest improvement in compliance. •Future research connecting guideline design to relevant patient outcomes is merited. Purpose To identify and characterize studies evaluating clinician compliance with infection-related guidelines, and to explore trends in guideline design and implementation strategies. Data sources PubMed database, April 2017. Followed the PRISMA Statement for systematic reviews. Study selection Scope was limited to studies reporting compliance with guidelines pertaining to the prevention, detection, and/or treatment of acute hospital-based infections. Initial search (1,499 titles) was reduced to 49 selected articles. Data extraction Extracted publication and guideline characteristics, outcome measures reported, and any results related to clinician compliance. Primary summary measures were frequencies and distributions of characteristics. Interventions that led to improved compliance results were analyzed to identify trends in guideline design and implementation. Results of data synthesis Of the 49 selected studies, 18 (37%), 13 (27%), and 10 (20%) focused on sepsis, pneumonia, and general infection, respectively. Six (12%), 17 (35%), and 26 (53%) studies assessed local, national, and international guidelines, respectively. Twenty studies (41%) reported 1-instance compliance results, 28 studies (57%) reported 2-instance compliance results (either before-and-after studies or control group studies), and 1 study (2%) described compliance qualitatively. Average absolute change in compliance for minimal, decision support, and multimodal interventions was 10%, 14%, and 25%, respectively. Twelve studies (24%) reported no patient outcome alongside compliance. Conclusions Multimodal interventions and quality improvement initiatives seem to produce the greatest improvement in compliance, but trends in other factors were inconsistent. Additional research is required to investigate these relationships and understand the implications behind various approaches to guideline design, communication, and implementation, in addition to effectiveness of protocol impact on relevant patient outcomes. To identify and characterize studies evaluating clinician compliance with infection-related guidelines, and to explore trends in guideline design and implementation strategies. PubMed database, April 2017. Followed the PRISMA Statement for systematic reviews. Scope was limited to studies reporting compliance with guidelines pertaining to the prevention, detection, and/or treatment of acute hospital-based infections. Initial search (1,499 titles) was reduced to 49 selected articles. Extracted publication and guideline characteristics, outcome measures reported, and any results related to clinician compliance. Primary summary measures were frequencies and distributions of characteristics. Interventions that led to improved compliance results were analyzed to identify trends in guideline design and implementation. Of the 49 selected studies, 18 (37%), 13 (27%), and 10 (20%) focused on sepsis, pneumonia, and general infection, respectively. Six (12%), 17 (35%), and 26 (53%) studies assessed local, national, and international guidelines, respectively. Twenty studies (41%) reported 1-instance compliance results, 28 studies (57%) reported 2-instance compliance results (either before-and-after studies or control group studies), and 1 study (2%) described compliance qualitatively. Average absolute change in compliance for minimal, decision support, and multimodal interventions was 10%, 14%, and 25%, respectively. Twelve studies (24%) reported no patient outcome alongside compliance. Multimodal interventions and quality improvement initiatives seem to produce the greatest improvement in compliance, but trends in other factors were inconsistent. Additional research is required to investigate these relationships and understand the implications behind various approaches to guideline design, communication, and implementation, in addition to effectiveness of protocol impact on relevant patient outcomes.}, number={8}, journal={AMERICAN JOURNAL OF INFECTION CONTROL}, author={McKenzie, Kendall E. and Mayorga, Maria E. and Miller, Kristen E. and Singh, Nishant and Arnold, Ryan C. and Romero-Brufau, Santiago}, year={2020}, month={Aug}, pages={940–947} }
 @article{velasquez_mayorga_ozaltin_2020, title={Prepositioning disaster relief supplies using robust optimization}, volume={52}, ISSN={["2472-5862"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85081951522&partnerID=MN8TOARS}, DOI={10.1080/24725854.2020.1725692}, abstractNote={Emergency disaster managers are concerned with responding to disasters in a timely and efficient manner. We are concerned with determining the location and amount of disaster relief supplies to be ...}, number={10}, journal={IISE TRANSACTIONS}, author={Velasquez, German A. and Mayorga, Maria E. and Ozaltin, Osman Y.}, year={2020}, month={Oct}, pages={1122–1140} }
 @article{powell_frerichs_townsley_mayorga_richmond_corbie-smith_wheeler_lich_2020, title={The potential impact of the Affordable Care Act and Medicaid expansion on reducing colorectal cancer screening disparities in African American males}, volume={15}, ISSN={["1932-6203"]}, DOI={10.1371/journal.pone.0226942}, abstractNote={Few investigations have explored the potential impact of the Affordable Care Act on health disparity outcomes in states that chose to forgo Medicaid expansion. Filling this evidence gap is pressing as Congress grapples with controversial healthcare legislation that could phase out Medicaid expansion. Colorectal cancer (CRC) is a commonly diagnosed, preventable cancer in the US that disproportionately burdens African American men and has substantial potential to be impacted by improved healthcare insurance coverage. Our objective was to estimate the impact of the Affordable Care Act (increasing insurance through health exchanges alone or with Medicaid expansion) on colorectal cancer outcomes and economic costs among African American and White males in North Carolina (NC), a state that did not expand Medicaid. We used an individual-based simulation model to estimate the impact of ACA (increasing insurance through health exchanges alone or with Medicaid expansion) on three CRC outcomes (screening, stage-specific incidence, and deaths) and economic costs among African American and White males in NC who were age-eligible for screening (between ages 50 and 75) during the study period, years of 2013-2023. Health exchanges and Medicaid expansion improved simulated CRC outcomes overall, though the impact was more substantial among AAs. Relative to health exchanges alone, Medicaid expansion would prevent between 7.1 to 25.5 CRC cases and 4.1 to 16.4 per 100,000 CRC cases among AA and White males, respectively. Our findings suggest policies that expanding affordable, quality healthcare coverage could have a demonstrable, cost-saving impact while reducing cancer disparities.}, number={1}, journal={PLOS ONE}, author={Powell, Wizdom and Frerichs, Leah and Townsley, Rachel and Mayorga, Maria and Richmond, Jennifer and Corbie-Smith, Giselle and Wheeler, Stephanie and Lich, Kristen Hassmiller}, year={2020}, month={Jan} }
 @article{diaz-garelli_strowd_lawson_mayorga_wells_lycan_topaloglu_2020, title={Workflow Differences Affect Data Accuracy in Oncologic EHRs: A First Step Toward Detangling the Diagnosis Data Babel}, volume={4}, ISSN={["2473-4276"]}, DOI={10.1200/CCI.19.00114}, abstractNote={PURPOSE Diagnosis (DX) information is key to clinical data reuse, yet accessible structured DX data often lack accuracy. Previous research hints at workflow differences in cancer DX entry, but their link to clinical data quality is unclear. We hypothesized that there is a statistically significant relationship between workflow-describing variables and DX data quality. METHODS We extracted DX data from encounter and order tables within our electronic health records (EHRs) for a cohort of patients with confirmed brain neoplasms. We built and optimized logistic regressions to predict the odds of fully accurate (ie, correct neoplasm type and anatomic site), inaccurate, and suboptimal (ie, vague) DX entry across clinical workflows. We selected our variables based on correlation strength of each outcome variable. RESULTS Both workflow and personnel variables were predictive of DX data quality. For example, a DX entered in departments other than oncology had up to 2.89 times higher odds of being accurate ( P < .0001) compared with an oncology department; an outpatient care location had up to 98% fewer odds of being inaccurate ( P < .0001), but had 458 times higher odds of being suboptimal ( P < .0001) compared with main campus, including the cancer center; and a DX recoded by a physician assistant had 85% fewer odds of being suboptimal ( P = .005) compared with those entered by physicians. CONCLUSION These results suggest that differences across clinical workflows and the clinical personnel producing EHR data affect clinical data quality. They also suggest that the need for specific structured DX data recording varies across clinical workflows and may be dependent on clinical information needs. Clinicians and researchers reusing oncologic data should consider such heterogeneity when conducting secondary analyses of EHR data.}, journal={JCO CLINICAL CANCER INFORMATICS}, author={Diaz-Garelli, Franck and Strowd, Roy and Lawson, Virginia L. and Mayorga, Maria E. and Wells, Brian J. and Lycan, Thomas W., Jr. and Topaloglu, Umit}, year={2020}, month={Jun}, pages={529–538} }
 @article{pearce_antani_mears_funk_mayorga_kurz_2019, title={An effective integer program for a general assembly line balancing problem with parallel workers and additional assignment restrictions}, volume={50}, ISSN={0278-6125}, url={http://dx.doi.org/10.1016/J.JMSY.2018.12.011}, DOI={10.1016/J.JMSY.2018.12.011}, abstractNote={Abstract The scope of the assembly line balancing problem in research is clear, with well-defined sets of assumptions, parameters, and objective functions. In application, these borders are frequently transgressed. Many of these deviations are internal to the assembly line balancing problem itself, arising from any of the physical or technological features in modern assembly lines. Other issues are founded in the tight coupling of assembly line balancing with external production planning and management problems, as assembly lines are at the intersection of multiple related problems in job sequencing, part flow logistics, worker safety, and quality. General assembly line balancing is devoted to studying the solution techniques necessary to model these applied line balancing problems. This article presents a complex line balancing problem based on the real production environment of our industrial partner, featuring several extensions for task-to-task relationships, station characteristics limiting assignment, and parallel worker zoning interactions. A heuristic, combining rank-position-weighting, last-fit-improvement and iterative blocking scheme, and an integer program that can manage multiple constraint types simultaneously, are developed. An experiment is conducted testing each of these new solution methods upon a battery of testbed problems, measuring solution quality, runtime, and achievement of feasibility. Results indicate that the integer programming model provides a viable solution method for those industries with access to commercial solvers.}, journal={Journal of Manufacturing Systems}, publisher={Elsevier BV}, author={Pearce, Bryan W. and Antani, Kavit and Mears, Laine and Funk, Kilian and Mayorga, Maria E. and Kurz, Mary E.}, year={2019}, month={Jan}, pages={180–192} }
 @misc{meghan c. o'leary_lich_gu_wheeler_coronado_bartelmann_lind_mayorga_davis_2019, title={Colorectal cancer screening in newly insured Medicaid members: a review of concurrent federal and state policies}, volume={19}, ISSN={["1472-6963"]}, DOI={10.1186/s12913-019-4113-2}, abstractNote={Colorectal cancer (CRC) screening is underutilized by Medicaid enrollees and the uninsured. Multiple national and state policies were enacted from 2010 to 2014 to increase access to Medicaid and to promote CRC screening among Medicaid enrollees. We aimed to determine the impact of these policies on screening initiation among newly enrolled Oregon Medicaid beneficiaries age-eligible for CRC screening. We identified national and state policies affecting Medicaid coverage and preventive services in Oregon during 2010–2014. We used Oregon Medicaid claims data from 2010 to 2015 to conduct a cohort analysis of enrollees who turned 50 and became age-eligible for CRC screening (a prevention milestone, and an age at which guideline-concordant screening can be assessed within a single year) during each year from 2010 to 2014. We calculated risk ratios to assess whether first year of Medicaid enrollment and/or year turned 50 was associated with CRC screening initiation. We identified 14,576 Oregon Medicaid enrollees who turned 50 during 2010–2014; 2429 (17%) completed CRC screening within 12 months after turning 50. Individuals newly enrolled in Medicaid in 2013 or 2014 were 1.58 and 1.31 times more likely, respectively, to initiate CRC screening than those enrolled by 2010. A primary care visit in the calendar year, having one or more chronic conditions, and being Hispanic was also associated with CRC screening initiation. The increased uptake of CRC screening in 2013 and 2014 is associated with the timing of policies such as Medicaid expansion, enhanced federal matching for preventive services offered to Medicaid enrollees without cost sharing, and formation of Medicaid accountable care organizations, which included CRC screening as an incentivized quality metric.}, journal={BMC HEALTH SERVICES RESEARCH}, author={Meghan C. O'Leary and Lich, Kristen Hassmiller and Gu, Yifan and Wheeler, Stephanie B. and Coronado, Gloria D. and Bartelmann, Sarah E. and Lind, Bonnie K. and Mayorga, Maria E. and Davis, Melinda M.}, year={2019}, month={May} }
 @article{lich_meghan c. o'leary_nambiar_townsley_mayorga_hicklin_frerichs_shafer_davis_wheeler_2019, title={Estimating the impact of insurance expansion on colorectal cancer and related costs in North Carolina: A population-level simulation analysis}, volume={129}, ISSN={["1096-0260"]}, url={http://dx.doi.org/10.1016/j.ypmed.2019.105847}, DOI={10.1016/j.ypmed.2019.105847}, abstractNote={Abstract Although screening is effective in reducing incidence, mortality, and costs of treating colorectal cancer (CRC), it remains underutilized, in part due to limited insurance access. We used microsimulation to estimate the health and financial effects of insurance expansion and reduction scenarios in North Carolina (NC). We simulated the full lifetime of a simulated population of 3,298,265 residents age-eligible for CRC screening (ages 50–75) during a 5-year period starting January 1, 2018, including polyp incidence and progression and CRC screening, diagnosis, treatment, and mortality. Insurance scenarios included: status quo, which in NC includes access to the Health Insurance Exchange (HIE) under the Affordable Care Act (ACA); no ACA; NC Medicaid expansion, and Medicare-for-all. The insurance expansion scenarios would increase percent up-to-date with screening by 0.3 and 7.1 percentage points for Medicaid expansion and Medicare-for-all, respectively, while insurance reduction would reduce percent up-to-date by 1.1 percentage points, compared to the status quo (51.7% up-to-date), at the end of the 5-year period. Throughout these individuals' lifetimes, this change in CRC screening/testing results in an estimated 498 CRC cases averted with Medicaid expansion and 6031 averted with Medicare-for-all, and an additional 1782 cases if health insurance gains associated with ACA are lost. Estimated cost savings – balancing increased CRC screening/testing costs against decreased cancer treatment costs – are approximately $30 M and $970 M for Medicaid expansion and Medicare-for-all scenarios, respectively, compared to status quo. Insurance expansion is likely to improve CRC screening both overall and in underserved populations while saving money, with the largest savings realized by Medicare.}, journal={PREVENTIVE MEDICINE}, author={Lich, Kristen Hassmiller and Meghan C. O'Leary and Nambiar, Siddhartha and Townsley, Rachel M. and Mayorga, Maria E. and Hicklin, Karen and Frerichs, Leah and Shafer, Paul R. and Davis, Melinda M. and Wheeler, Stephanie B.}, year={2019}, month={Dec} }
 @article{enayati_mayorga_toro-diaz_albert_2019, title={Identifying trade-offs in equity and efficiency for simultaneously optimizing location and multipriority dispatch of ambulances}, volume={26}, ISSN={["1475-3995"]}, DOI={10.1111/itor.12590}, number={2}, journal={INTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH}, author={Enayati, Shakiba and Mayorga, Maria E. and Toro-Diaz, Hector and Albert, Laura A.}, year={2019}, month={Mar}, pages={415–438} }
 @article{davis_nambiar_mayorga_sullivan_hicklin_meghan c. o'leary_dillon_lich_gu_lind_et al._2019, title={Mailed FIT (fecal immunochemical test), navigation or patient reminders? Using microsimulation to inform selection of interventions to increase colorectal cancer screening in Medicaid enrollees}, volume={129}, ISSN={["1096-0260"]}, url={http://dx.doi.org/10.1016/j.ypmed.2019.105836}, DOI={10.1016/j.ypmed.2019.105836}, abstractNote={Abstract Colorectal cancer (CRC) can be effectively prevented or detected with guideline concordant screening, yet Medicaid enrollees experience disparities. We used microsimulation to project CRC screening patterns, CRC cases averted, and life-years gained in the population of 68,077 Oregon Medicaid enrollees 50–64 over a five year period starting in January 2019. The simulation estimated the cost-effectiveness of five intervention scenarios - academic detailing plus provider audit and feedback (Detailing+), patient reminders (Reminders), mailing a Fecal Immunochemical Test (FIT) directly to the patient's home (Mailed FIT), patient navigation (Navigation), and mailed FIT with Navigation (Mailed FIT + Navigation) – compared to usual care. Each intervention scenario raised CRC screening rates compared to usual care, with improvements as high as 11.6 percentage points (Mailed FIT + Navigation) and as low as 2.5 percentage points (Reminders) after one year. Compared to usual care, Mailed FIT + Navigation would raise CRC screening rates 20.2 percentage points after five years - averting nearly 77 cancer cases (a reduction of 113 per 100,000) and exceeding national screening targets. Over a five year period, Reminders, Mailed FIT and Mailed FIT + Navigation were expected to be cost effective if stakeholders were willing to pay $230 or less per additional year up-to-date (at a cost of $22, $59, and $227 respectively), whereas Detailing+ and Navigation were more costly for the same benefits. To approach national CRC screening targets, health system stakeholders are encouraged to implement Mailed FIT with or without Navigation and Reminders.}, journal={PREVENTIVE MEDICINE}, author={Davis, Melinda M. and Nambiar, Siddhartha and Mayorga, Maria E. and Sullivan, Eliana and Hicklin, Karen and Meghan C. O'Leary and Dillon, Kristen and Lich, Kristen Hassmiller and Gu, Yifan and Lind, Bonnie K. and et al.}, year={2019}, month={Dec} }
 @misc{fishbein_nambiar_mckenzie_mayorga_miller_tran_schubel_agor_kim_capan_2019, title={Objective measures of workload in healthcare: a narrative review}, volume={33}, ISSN={["1758-6542"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85077284434&partnerID=MN8TOARS}, DOI={10.1108/IJHCQA-12-2018-0288}, abstractNote={Purpose Workload is a critical concept in the evaluation of performance and quality in healthcare systems, but its definition relies on the perspective (e.g. individual clinician-level vs unit-level workload) and type of available metrics (e.g. objective vs subjective measures). The purpose of this paper is to provide an overview of objective measures of workload associated with direct care delivery in tertiary healthcare settings, with a focus on measures that can be obtained from electronic records to inform operationalization of workload measurement. Design/methodology/approach Relevant papers published between January 2008 and July 2018 were identified through a search in Pubmed and Compendex databases using the Sample, Phenomenon of Interest, Design, Evaluation, Research Type framework. Identified measures were classified into four levels of workload: task, patient, clinician and unit. Findings Of 30 papers reviewed, 9 used task-level metrics, 14 used patient-level metrics, 7 used clinician-level metrics and 20 used unit-level metrics. Key objective measures of workload include: patient turnover ( n =9), volume of patients ( n =6), acuity ( n =6), nurse-to-patient ratios ( n =5) and direct care time ( n =5). Several methods for operationalization of these metrics into measurement tools were identified. Originality/value This review highlights the key objective workload measures available in electronic records that can be utilized to develop an operational approach for quantifying workload. Insights gained from this review can inform the design of processes to track workload and mitigate the effects of increased workload on patient outcomes and clinician performance.}, number={1}, journal={INTERNATIONAL JOURNAL OF HEALTH CARE QUALITY ASSURANCE}, author={Fishbein, Daniela and Nambiar, Siddhartha and McKenzie, Kendall and Mayorga, Maria and Miller, Kristen and Tran, Kevin and Schubel, Laura and Agor, Joseph and Kim, Tracy and Capan, Muge}, year={2019}, month={Dec}, pages={1–17} }
 @article{velasquez_mayorga_cruz_2019, title={Prepositioning inventory for disasters: a robust and equitable model}, volume={41}, ISSN={["1436-6304"]}, DOI={10.1007/s00291-019-00554-z}, number={3}, journal={OR SPECTRUM}, author={Velasquez, German A. and Mayorga, Maria E. and Cruz, Eduardo A. R.}, year={2019}, month={Sep}, pages={757–785} }
 @article{enayati_ozaltin_mayorga_saydam_2018, title={Ambulance redeployment and dispatching under uncertainty with personnel workload limitations}, volume={50}, ISSN={["2472-5862"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85048249953&partnerID=MN8TOARS}, DOI={10.1080/24725854.2018.1446105}, abstractNote={Emergency Medical Services (EMS) managers are concerned with responding to emergency calls in a timely manner. Redeployment and dispatching strategies can be used to improve coverage that pertains ...}, number={9}, journal={IISE TRANSACTIONS}, author={Enayati, Shakiba and Ozaltin, Osman Y. and Mayorga, Maria E. and Saydam, Cem}, year={2018}, pages={777–788} }
 @article{maillart_mayorga_2018, title={Introduction to the Special Issue on Advancing Health Services}, volume={10}, ISSN={["2164-3970"]}, DOI={10.1287/serv.2018.0225}, number={3}, journal={SERVICE SCIENCE}, author={Maillart, Lisa M. and Mayorga, Maria E.}, year={2018}, month={Sep}, pages={V-VII} }
 @article{nasrollahzadeh_khademi_mayorga_2018, title={Real-Time Ambulance Dispatching and Relocation}, volume={20}, ISSN={1523-4614 1526-5498}, url={http://dx.doi.org/10.1287/msom.2017.0649}, DOI={10.1287/msom.2017.0649}, abstractNote={In this study, we develop a flexible optimization framework for real-time ambulance dispatching and relocation. In addition to ambulance redeployment, we consider a general dispatching and relocation strategy by which the decision maker has the option to (i) select any available ambulance to dispatch to a call or to queue the call and (ii) send an idle ambulance to cover the location of an ambulance just dispatched to a call. We formulate the problem as a stochastic dynamic program, and, because the state space is unbounded, an approximate dynamic programming (ADP) framework is developed to generate high-quality solutions. We assess the quality of our solutions by developing a lower bound on the expected response time and computing a lower bound on the expected fraction of late calls of any relocation policy. We test the performance of our policies and available benchmarks on an emergency medical services system in Mecklenburg County, North Carolina. The results show that our policies are near optimal and significantly outperform available benchmarks. In particular, our ADP policy reduces the expected response time and fraction of high-priority late calls by 12% and 30.6%, respectively, over the best available static benchmarks in the case study. Moreover, the results provide insights on the contribution of each dispatching, redeployment, and reallocation strategy. The online appendix is available at https://doi.org/10.1287/msom.2017.0649 .}, number={3}, journal={Manufacturing & Service Operations Management}, publisher={Institute for Operations Research and the Management Sciences (INFORMS)}, author={Nasrollahzadeh, Amir Ali and Khademi, Amin and Mayorga, Maria E.}, year={2018}, month={Jul}, pages={467–480} }
 @article{enayati_mayorga_rajagopalan_saydam_2018, title={Real-time ambulance redeployment approach to improve service coverage with fair and restricted workload for EMS providers}, volume={79}, ISSN={0305-0483}, url={http://dx.doi.org/10.1016/j.omega.2017.08.001}, DOI={10.1016/j.omega.2017.08.001}, abstractNote={Abstract Emergency Medical Services (EMS) managers are concerned with providing maximum possible coverage in their service area. As emergency calls arrive into the EMS system, some ambulances become unavailable. Redeployment deals with a dynamic relocation of available ambulances so as to compensate for the loss in coverage due to busy ambulances. Unsystematic redeployment can impose superfluous workload and result in unnecessary fatigue for EMS personnel. This paper develops a real-time approach to maximize coverage with minimum possible total travel time, considering accumulated workload restrictions for personnel in a shift. While in the past real-time redeployment has been hindered due to computational issues, we find a solution to this problem by combining two computationally inexpensive models into a single framework. The proposed approach requires only knowledge of the current state of the system in a real-time manner and, due to very short run time, is applicable in practice. The performance of our real-time approach is evaluated by a discrete-event simulation developed for a large real dataset and is compared with two benchmarks in the literature; an existing dynamic redeployment approach and a static policy. The results show statistically significant improvement in average coverage, while restricting accumulated workload for EMS personnel as well as providing more evenly distributed workload between ambulances in a shift.}, journal={Omega}, publisher={Elsevier BV}, author={Enayati, Shakiba and Mayorga, Maria E. and Rajagopalan, Hari K. and Saydam, Cem}, year={2018}, month={Sep}, pages={67–80} }
 @article{ansari_mclay_mayorga_2017, title={A Maximum Expected Covering Problem for District Design}, volume={51}, ISSN={0041-1655 1526-5447}, url={http://dx.doi.org/10.1287/trsc.2015.0610}, DOI={10.1287/trsc.2015.0610}, abstractNote={The optimal location of ambulances in a geographic region is interrelated with how the ambulances are dispatched to patients. Papers in the literature often treat the location and dispatching of ambulance separately. In this paper, we propose a novel mixed integer linear programming (MILP) model that determines how to locate and dispatch ambulances through district design. The model allows for uncertainty in both ambulance travel times and ambulance availability, and it maximizes the coverage level, i.e., the fraction of high-priority calls that can be responded to within a fixed-time threshold. The proposed MILP model determines the stations where ambulances should be located and assigns each call location to the open ambulance stations according to a preference list. The preference list is a rank ordering of the ambulances to assign to patients at a call location, from the most to the least preferred. The preference lists partition the region into a series of response districts that depend on ambulance availability, and the model balances the workload among the servers and maintains contiguity in the first priority response districts. The underlying ambulance queuing dynamics introduce nonlinearities to the model. To maintain a linear model, we use a Hypercube approximation model to estimate several of the inputs, and we provide an iterative algorithm to update the input parameters and solve the resulting MILP model. A computational example illustrates the modeling paradigm and solution algorithm using a real-world example. The results suggest that the reduction in coverage to maintain contiguity and balanced workloads among the ambulances is small.}, number={1}, journal={Transportation Science}, publisher={Institute for Operations Research and the Management Sciences (INFORMS)}, author={Ansari, Sardar and McLay, Laura Albert and Mayorga, Maria E.}, year={2017}, month={Feb}, pages={376–390} }
 @article{yi_mayorga_lich_pearson_2017, title={Changes in cigarette smoking initiation, cessation, and relapse among US adults: a comparison of two longitudinal samples}, volume={15}, ISSN={["1617-9625"]}, DOI={10.1186/s12971-017-0121-3}, abstractNote={The tobacco epidemic in the U.S. has matured in the past decade. However, due to rapidly changing social policy and commercial environments, tailored prevention and interventions are needed to support further reduction in smoking.Using Tobacco Use Supplement to the Current Population Survey (TUS-CPS) 2002-2003 and 2010-2011 longitudinal cohorts, five smoking states are defined including daily-heavy, daily-light, non-daily, former and non-smoker. We quantified the changes between smoking states for the two longitudinal cohorts, and used a series of multivariable logistic regression models to examine the association of socio-demographic attributes and initial smoking states on smoking initiation, cessation, and relapse between waves within each cohort.The prevalence of adult heavy smoking decreased from 9.9% (95% CI: 9.6%, 10.2%) in 2002 to 7.1% (95% CI: 6.9%, 7.4%) in 2010. Non-daily smokers were less likely to quit in the 2010-2011 cohort than the 2002-2003 cohort (37.0% vs. 44.9%). Gender, age group, smoker type, race and marital status exhibit similar patterns in terms of their association to the odds of initiation, cessation and relapse between the two cohorts, while education groups showed some inconsistent results between the two cohorts regarding the odds of cessation.Transitions between smoking states are complex and increasingly unstable, requiring a holistic, population-based perspective to understand the stocks and flows that ultimately dictate the public health impact of cigarette smoking behavior. This knowledge helps to identify groups in need of increased tobacco control prevention and intervention efforts.}, journal={TOBACCO INDUCED DISEASES}, author={Yi, Zinan and Mayorga, Maria E. and Lich, Kristen Hassmiller and Pearson, Jennifer L.}, year={2017}, month={Mar} }
 @article{hassmiller lich_cornejo_mayorga_pignone_tangka_richardson_kuo_meyer_hall_smith_et al._2017, title={Cost-Effectiveness Analysis of Four Simulated Colorectal Cancer Screening Interventions, North Carolina}, volume={14}, ISSN={1545-1151}, url={http://dx.doi.org/10.5888/pcd14.160158}, DOI={10.5888/pcd14.160158}, abstractNote={Colorectal cancer (CRC) screening rates are suboptimal, particularly among the uninsured and the under-insured and among rural and African American populations. Little guidance is available for state-level decision makers to use to prioritize investment in evidence-based interventions to improve their population's health. The objective of this study was to demonstrate use of a simulation model that incorporates synthetic census data and claims-based statistical models to project screening behavior in North Carolina.We used individual-based modeling to simulate and compare intervention costs and results under 4 evidence-based and stakeholder-informed intervention scenarios for a 10-year intervention window, from January 1, 2014, through December 31, 2023. We compared the proportion of people living in North Carolina who were aged 50 to 75 years at some point during the window (that is, age-eligible for screening) who were up to date with CRC screening recommendations across intervention scenarios, both overall and among groups with documented disparities in receipt of screening.We estimated that the costs of the 4 intervention scenarios considered would range from $1.6 million to $3.75 million. Our model showed that mailed reminders for Medicaid enrollees, mass media campaigns targeting African Americans, and colonoscopy vouchers for the uninsured reduced disparities in receipt of screening by 2023, but produced only small increases in overall screening rates (0.2-0.5 percentage-point increases in the percentage of age-eligible adults who were up to date with CRC screening recommendations). Increased screenings ranged from 41,709 additional life-years up to date with screening for the voucher intervention to 145,821 for the mass media intervention. Reminders mailed to Medicaid enrollees and the mass media campaign for African Americans were the most cost-effective interventions, with costs per additional life-year up to date with screening of $25 or less. The intervention expanding the number of endoscopy facilities cost more than the other 3 interventions and was less effective in increasing CRC screening.Cost-effective CRC screening interventions targeting observed disparities are available, but substantial investment (more than $3.75 million) and additional approaches beyond those considered here are required to realize greater increases population-wide.}, journal={Preventing Chronic Disease}, publisher={Centers for Disease Control and Prevention (CDC)}, author={Hassmiller Lich, Kristen and Cornejo, David A. and Mayorga, Maria E. and Pignone, Michael and Tangka, Florence K.L. and Richardson, Lisa C. and Kuo, Tzy-Mey and Meyer, Anne-Marie and Hall, Ingrid J. and Smith, Judith Lee and et al.}, year={2017}, month={Feb} }
 @inbook{townsley_mayorga_barritt iv_orman_2017, title={Forecasting Recipient Outcomes of Deceased Donor Livers}, ISBN={9789813220843 9789813220850}, url={http://dx.doi.org/10.1142/9789813220850_0008}, DOI={10.1142/9789813220850_0008}, booktitle={Stochastic Modeling and Analytics in Healthcare Delivery Systems}, publisher={WORLD SCIENTIFIC}, author={Townsley, Rachel M. and Mayorga, Maria E. and Barritt IV, A. Sidney and Orman, Eric}, year={2017}, month={Sep}, pages={189–209} }
 @article{wheeler_kuo_meyer_martens_hassmiller lich_tangka_richardson_hall_smith_mayorga_et al._2017, title={Multilevel predictors of colorectal cancer testing modality among publicly and privately insured people turning 50}, volume={6}, ISSN={2211-3355}, url={http://dx.doi.org/10.1016/j.pmedr.2016.11.019}, DOI={10.1016/j.pmedr.2016.11.019}, abstractNote={Understanding multilevel predictors of colorectal cancer (CRC) screening test modality can help inform screening program design and implementation. We used North Carolina Medicare, Medicaid, and private, commercially available, health plan insurance claims data from 2003 to 2008 to ascertain CRC test modality among people who received CRC screening around their 50th birthday, when guidelines recommend that screening should commence for normal risk individuals. We ascertained receipt of colonoscopy, fecal occult blood test (FOBT) and fecal immunochemical test (FIT) from billing codes. Person-level and county-level contextual variables were included in multilevel random intercepts models to understand predictors of CRC test modality, stratified by insurance type. Of 12,570 publicly-insured persons turning 50 during the study period who received CRC testing, 57% received colonoscopy, whereas 43% received FOBT/FIT, with significant regional variation. In multivariable models, females with public insurance had lower odds of colonoscopy than males (odds ratio [OR] = 0.68; p < 0.05). Of 56,151 privately-insured persons turning 50 years old who received CRC testing, 42% received colonoscopy, whereas 58% received FOBT/FIT, with significant regional variation. In multivariable models, females with private insurance had lower odds of colonoscopy than males (OR = 0.43; p < 0.05). People living 10-15 miles away from endoscopy facilities also had lower odds of colonoscopy than those living within 5 miles (OR = 0.91; p < 0.05). Both colonoscopy and FOBT/FIT are widely used in North Carolina among insured persons newly age-eligible for screening. The high level of FOBT/FIT use among privately insured persons and women suggests that renewed emphasis on FOBT/FIT as a viable screening alternative to colonoscopy may be important.}, journal={Preventive Medicine Reports}, publisher={Elsevier BV}, author={Wheeler, Stephanie B. and Kuo, Tzy-Mey and Meyer, Anne Marie and Martens, Christa E. and Hassmiller Lich, Kristen M. and Tangka, Florence K.L. and Richardson, Lisa C. and Hall, Ingrid J. and Smith, Judith Lee and Mayorga, Maria E. and et al.}, year={2017}, month={Jun}, pages={9–16} }
 @inproceedings{agor_mckenzie_mayorga_ozaltin_parikh_huddleston_2017, title={Simulating triage of patients into an internal medicine department to validate the use of an optimization-based workload score}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85044522866&partnerID=MN8TOARS}, DOI={10.1109/wsc.2017.8248011}, booktitle={2017 winter simulation conference (wsc)}, author={Agor, J. and McKenzie, K. and Mayorga, Maria and Ozaltin, Osman and Parikh, R. S. and Huddleston, J.}, year={2017}, pages={2881–2892} }
 @article{mayorga_lodree_wolczynski_2017, title={The optimal assignment of spontaneous volunteers}, volume={68}, ISSN={0160-5682 1476-9360}, url={http://dx.doi.org/10.1057/s41274-017-0219-2}, DOI={10.1057/s41274-017-0219-2}, abstractNote={Spontaneous volunteers are ordinary citizens who assist in disaster relief efforts, while they are a great resource they also pose a difficult logistical challenge. Unlike classical labor assignment problems, the management of these volunteers is characterized by uncertainty regarding the size, availability, and commitment of the labor pool. We model this problem as a multi-server queueing system with both stochastic server arrival and abandonment. This model is intended to be applied to the relatively stable work associated with recovery efforts, e.g., debris clearing. We model this system as a continuous time Markov decision process and compare the optimal policy to several common-sense heuristics; one of which performs close to optimal and makes a practical alternative. We conduct extensive sensitivity analysis around model parameters and assumptions.}, number={9}, journal={Journal of the Operational Research Society}, publisher={Informa UK Limited}, author={Mayorga, Maria E. and Lodree, Emmett J. and Wolczynski, Justin}, year={2017}, month={Sep}, pages={1106–1116} }
 @article{yi_mayorga_orman_wheeler_hayashi_barritt_2017, title={Trends in Characteristics of Patients Listed for Liver Transplantation Will Lead to Higher Rates of Waitlist Removal Due to Clinical Deterioration}, volume={101}, ISSN={0041-1337}, url={http://dx.doi.org/10.1097/TP.0000000000001851}, DOI={10.1097/TP.0000000000001851}, abstractNote={Changes in the epidemiology of end-stage liver disease may lead to increased risk of dropout from the liver transplant waitlist. Anticipating the future of liver transplant waitlist characteristics is vital when considering organ allocation policy.We performed a discrete event simulation to forecast patient characteristics and rate of waitlist dropout. Estimates were simulated from 2015 to 2025. The model was informed by data from the Organ Procurement and Transplant Network, 2003 to 2014. National data are estimated along with forecasts for 2 regions.Nonalcoholic steatohepatitis will increase from 18% of waitlist additions to 22% by 2025. Hepatitis C will fall from 30% to 21%. Listings over age 60 years will increase from 36% to 48%. The hazard of dropout will increase from 41% to 46% nationally. Wait times for transplant for patients listed with a Model for End-Stage Liver Disease (MELD) between 22 and 27 will double. Region 5, which transplants at relatively higher MELD scores, will experience an increase from 53% to 64% waitlist dropout. Region 11, which transplants at lower MELD scores, will have an increase in waitlist dropout from 30% to 44%.The liver transplant waitlist size will remain static over the next decade due to patient dropout. Liver transplant candidates will be older, more likely to have nonalcoholic steatohepatitis and will wait for transplantation longer even when listed at a competitive MELD score. There will continue to be significant heterogeneity among transplant regions where some patients will be more likely to drop out of the waitlist than receive a transplant.}, number={10}, journal={Transplantation}, publisher={Ovid Technologies (Wolters Kluwer Health)}, author={Yi, Zinan and Mayorga, Maria E. and Orman, Eric S. and Wheeler, Stephanie B. and Hayashi, Paul H. and Barritt, A. Sidney, 4th}, year={2017}, month={Oct}, pages={2368–2374} }
 @inproceedings{mayorga_reifsnider_wheeler_kohler_2016, title={A Discrete event simulation model to estimate population level health and economic impacts of smoking cessation interventions}, booktitle={2016 10th european conference on antennas and propagation (eucap)}, author={Mayorga, M. E. and Reifsnider, O. S. and Wheeler, S. B. and Kohler, R. E.}, year={2016}, pages={1257–1268} }
 @inproceedings{goodarzi_mckenzie_nataraj_ivy_mayorga_mason_tejada_2016, title={A Framework for modeling the complex interaction between breast cancer and diabetes}, DOI={10.1109/wsc.2014.7019981}, booktitle={2016 10th european conference on antennas and propagation (eucap)}, author={Goodarzi, S. H. and McKenzie, K. and Nataraj, N. and Ivy, J. S. and Mayorga, Maria and Mason, J. and Tejada, J.}, year={2016}, pages={1245–1256} }
 @article{sudtachat_mayorga_mclay_2016, title={A nested-compliance table policy for emergency medical service systems under relocation}, volume={58}, ISSN={["0305-0483"]}, DOI={10.1016/j.omega.2015.06.001}, abstractNote={Abstract The goal of Emergency Medical Service (EMS) systems is to provide rapid response to emergency calls in order to save lives. This paper proposes a relocation strategy to improve the performance of EMS systems. In practice, EMS systems often use a compliance table to relocate ambulances. A compliance table specifies ambulance base stations as a function of the state of the system. We consider a nested-compliance table, which restricts the number of relocations that can occur simultaneously. We formulate the nested-compliance table model as an integer programming model in order to maximize expected coverage. We determine an optimal nested-compliance table policy using steady state probabilities of a Markov chain model with relocation as input parameters. These parameter approximations are independent of the exact compliance table used. We assume that there is a single type of medical unit, single call priority, and no patient queue. We validate the model by applying the nested-compliance table policies in a simulated system using real-world data. The numerical results show the benefit of our model over a static policy based on the adjusted maximum expected covering location problem (AMEXCLP).}, journal={OMEGA-INTERNATIONAL JOURNAL OF MANAGEMENT SCIENCE}, author={Sudtachat, Kanchala and Mayorga, Maria E. and Mclay, Laura A.}, year={2016}, month={Jan}, pages={154–168} }
 @article{zaffar_rajagopalan_saydam_mayorga_sharer_2016, title={Coverage, survivability or response time: A comparative study of performance statistics used in ambulance location models via simulation–optimization}, volume={11}, ISSN={2211-6923}, url={http://dx.doi.org/10.1016/j.orhc.2016.08.001}, DOI={10.1016/j.orhc.2016.08.001}, abstractNote={Abstract Rapid response to medical emergencies is one of the main goals of Emergency Medical Service (EMS) systems. Ability to provide timely response is affected by fleet size and the locations of the ambulances. Literature on ambulance location has been dominated by models which either maximize coverage, or guarantee coverage within some threshold. Recent work has shifted the objective from maximizing coverage to improving patient survivability. In this paper we compare the performance of three recent ambulance location model objectives by applying a simulation–optimization framework. Our findings show that the maximum survivability objective performs better in both survivability and coverage metrics. Further, the results also support using the survivability objective for resource constrained ambulance operators.}, journal={Operations Research for Health Care}, publisher={Elsevier BV}, author={Zaffar, Muhammad Adeel and Rajagopalan, Hari K. and Saydam, Cem and Mayorga, Maria and Sharer, Elizabeth}, year={2016}, month={Dec}, pages={1–12} }
 @inproceedings{cornejo_mayorga_lich_2016, title={Creating common patients and evaluating indiviual results: issues in indivual simulation for health policy analysis}, booktitle={2016 10th european conference on antennas and propagation (eucap)}, author={Cornejo, D. and Mayorga, M. E. and Lich, K. H.}, year={2016}, pages={1387–1398} }
 @inproceedings{agor_mckenzie_ozaltin_mayorga_parikh_huddleston_2016, title={Simulation of triaging patients into an internal medicine department to validate the use of an optimization based workload score}, volume={0}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-85014275794&partnerID=MN8TOARS}, DOI={10.1109/wsc.2016.7822411}, booktitle={2016 winter simulation conference (wsc)}, author={Agor, J. and McKenzie, K. and Ozaltin, Osman and Mayorga, Maria and Parikh, R. S. and Huddleston, J.}, year={2016}, pages={3708–3709} }
 @article{yi_mayorga_wheeler_hayashi_barritt_orman_2016, title={The numbers of new waitlist registrants and removals are outpacing the number of liver transplants: National trends and regional variation from 2003 through 2014}, volume={64}, journal={Hepatology}, author={Yi, Z. A. and Mayorga, M. and Wheeler, S. B. and Hayashi, P. H. and Barritt, A. S. and Orman, E. S.}, year={2016}, pages={701A–701} }
 @article{orman_mayorga_wheeler_townsley_toro-diaz_hayashi_sidney barritt_2015, title={Declining liver graft quality threatens the future of liver transplantation in the United States}, volume={21}, ISSN={1527-6465}, url={http://dx.doi.org/10.1002/lt.24160}, DOI={10.1002/lt.24160}, abstractNote={National liver transplantation (LT) volume has declined since 2006, in part because of worsening donor organ quality. Trends that degrade organ quality are expected to continue over the next 2 decades. We used the United Network for Organ Sharing (UNOS) database to inform a 20-year discrete event simulation estimating LT volume from 2010 to 2030. Data to inform the model were obtained from deceased organ donors between 2000 and 2009. If donor liver utilization practices remain constant, utilization will fall from 78% to 44% by 2030, resulting in 2230 fewer LTs. If transplant centers increase their risk tolerance for marginal grafts, utilization would decrease to 48%. The institution of "opt-out" organ donation policies to increase the donor pool would still result in 1380 to 1866 fewer transplants. Ex vivo perfusion techniques that increase the use of marginal donor livers may stabilize LT volume. Otherwise, the number of LTs in the United States will decrease substantially over the next 15 years. In conclusion, the transplant community will need to accept inferior grafts and potentially worse posttransplant outcomes and/or develop new strategies for increasing organ donation and utilization in order to maintain the number of LTs at the current level.}, number={8}, journal={Liver Transplantation}, publisher={Wiley}, author={Orman, Eric S. and Mayorga, Maria E. and Wheeler, Stephanie B. and Townsley, Rachel M. and Toro-Diaz, Hector H. and Hayashi, Paul H. and Sidney Barritt, A., IV}, year={2015}, month={Jul}, pages={1040–1050} }
 @article{lynch_baker_korte_mauldin_mayorga_hunt_2015, title={Increasing Prevalence of Diabetes During Pregnancy in South Carolina}, volume={24}, ISSN={["1931-843X"]}, url={https://www-liebertpub-com.prox.lib.ncsu.edu/doi/10.1089/jwh.2014.4968}, DOI={10.1089/jwh.2014.4968}, abstractNote={Background: The objective of our study was to examine the prevalence of diabetes during pregnancy at the population level in SC from January 1996 through December 2008. Methods: The study included 387,720 non-Hispanic white (NHW), 232,278 non-Hispanic black (NHB), and 43,454 Hispanic live singleton births. Maternal inpatient hospital discharge codes from delivery (91.59%) and prenatal information (i.e., Medicaid [42.91%] and SC State Health Plan [SHP] [5.98%]) were linked to birth certificate data. Diabetes during pregnancy included gestational and preexisting, defined by prenatal and maternal inpatient International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) diagnostic codes (i.e., 64801–64802, 64881–64882, or 25000–25092) or report on the birth certificate. Results: Diabetes prevalence from any source increased from 5.02% (95% confidence interval [CI]: 4.82–5.22) in 1996 to 8.37% (95% CI: 8.15–8.60) in 2008. Diabetes prevalence, standardized for maternal age and race/ethnicity from 1996 through 2008, increased from 3.38% (95% CI: 3.29–3.47) to 5.81% (95% CI: 5.71–5.91) using birth certificate data, from 3.99% (95% CI: 3.89–4.10) to 6.69% (95% CI: 6.58–6.80) using hospital discharge data, and from 4.74% (95% CI: 4.52–4.96) to 8.82% (95% CI: 8.61–9.03) using Medicaid data. Comparing birth certificate to hospital discharge, Medicaid, and SHP data, Cohen's kappa in 2008 was 0.73 (95% CI: 0.72–0.75), 0.64 (95% CI: 0.62–0.66), and 0.59 (95% CI: 0.54–0.65), respectively. Conclusions: An increasing prevalence of diabetes during pregnancy is reported, as well as substantial lack of agreement in reporting of diabetes prevalence across administrative databases. Prevalence of reported diabetes during pregnancy is impacted by screening, diagnostic, and reporting practices across different data sources, as well as by actual changes in prevalence over time.}, number={4}, journal={Journal of Women’s Health}, author={Lynch, C.P. and Baker, N. and Korte, J.E. and Mauldin, J.G. and Mayorga, M.E. and Hunt, K.J.}, year={2015}, month={Apr}, pages={316–323} }
 @article{toro-díaz_mayorga_mclay_rajagopalan_saydam_2015, title={Reducing disparities in large-scale emergency medical service systems}, volume={66}, ISSN={0160-5682 1476-9360}, url={http://dx.doi.org/10.1057/jors.2014.83}, DOI={10.1057/jors.2014.83}, abstractNote={Emergency Medical Service (EMS) systems operate under the pressure of knowing that human lives might be directly at stake. In the public eye there is a natural expectation of efficient response. There is abundant literature on the topic of efficient planning of EMS systems (maximizing expected coverage or minimizing response time). Other objectives have been considered but the literature available is very sparse compared to efficiency-based works. Furthermore, while real size EMS systems have been studied, the use of exact models is usually hindered by the amount of computational time required to obtain solutions. We approach the planning of large-scale EMS systems including fairness considerations using a Tabu Search-based heuristic with an embedded approximation procedure for the queuing submodel. This allows for the analysis of large-scale real systems, extending the approach in which strategic decisions (location) and operative decisions (dispatching) are combined to balance efficiency and fairness.}, number={7}, journal={Journal of the Operational Research Society}, publisher={Informa UK Limited}, author={Toro-Díaz, Hector and Mayorga, Maria E and McLay, Laura A and Rajagopalan, Hari K and Saydam, Cem}, year={2015}, month={Jul}, pages={1169–1181} }
 @article{mayorga_reifsnider_yi_hunt_2015, title={Trends in BMI and obesity in U.S. women of childbearing age during the period of 1980–2010}, volume={4}, ISSN={2047-6965 2047-6973}, url={http://dx.doi.org/10.1057/hs.2014.29}, DOI={10.1057/hs.2014.29}, abstractNote={Statistical analyses and simulation are combined to provide insights about the trends in weight gain in U.S. women of childbearing age. This population is of specific interest because it is central to understanding the trans-generational effects of obesity in future U.S. populations. We estimated BMI trends among women of childbearing age during the period 1980–2010 using the National Health and Nutrition Examination Survey (NHANES) data. Then, we introduce a secondary approach; using the BMI profile of women by age and race as it was before the onset of the obesity epidemic (1970–1980) we project the BMI of women during the period 1980–2010 using U.S. Census demographic information. Hence, we compare the real-world situation to the age-adjusted scenario without the obesity epidemic. We found that there are differences in weight gain in black and white women, the racial disparity has worsened over time and that changes in the racial disparity were not because of changes in the age structure of the population.}, number={3}, journal={Health Systems}, publisher={Informa UK Limited}, author={Mayorga, Maria E and Reifsnider, Odette S and Yi, Zinan and Hunt, Kelly J}, year={2015}, month={Nov}, pages={176–186} }
 @article{chanta_mayorga_mclay_2014, title={Improving emergency service in rural areas: a bi-objective covering location model for EMS systems}, volume={221}, ISSN={0254-5330 1572-9338}, url={http://dx.doi.org/10.1007/s10479-011-0972-6}, DOI={10.1007/s10479-011-0972-6}, number={1}, journal={Annals of Operations Research}, publisher={Springer Science and Business Media LLC}, author={Chanta, Sunarin and Mayorga, Maria E. and McLay, Laura A.}, year={2014}, pages={133–159} }
 @article{toro-díaz_mayorga_barritt_orman_wheeler_2014, title={Predicting Liver Transplant Capacity Using Discrete Event Simulation}, volume={35}, ISSN={0272-989X 1552-681X}, url={http://dx.doi.org/10.1177/0272989x14559055}, DOI={10.1177/0272989x14559055}, abstractNote={The number of liver transplants (LTs) performed in the US increased until 2006 but has since declined despite an ongoing increase in demand. This decline may be due in part to decreased donor liver quality and increasing discard of poor-quality livers. We constructed a discrete event simulation (DES) model informed by current donor characteristics to predict future LT trends through the year 2030. The data source for our model is the United Network for Organ Sharing database, which contains patient-level information on all organ transplants performed in the US. Previous analysis showed that liver discard is increasing and that discarded organs are more often from donors who are older, are obese, have diabetes, and donated after cardiac death. Given that the prevalence of these factors is increasing, the DES model quantifies the reduction in the number of LTs performed through 2030. In addition, the model estimatesthe total number of future donors needed to maintain the current volume of LTs and the effect of a hypothetical scenario of improved reperfusion technology.We also forecast the number of patients on the waiting list and compare this with the estimated number of LTs to illustrate the impact that decreased LTs will have on patients needing transplants. By altering assumptions about the future donor pool, this model can be used to develop policy interventions to prevent a further decline in this lifesaving therapy. To our knowledge, there are no similar predictive models of future LT use based on epidemiological trends.}, number={6}, journal={Medical Decision Making}, publisher={SAGE Publications}, author={Toro-Díaz, Hector and Mayorga, Maria E. and Barritt, A. Sidney and Orman, Eric S. and Wheeler, Stephanie B.}, year={2014}, month={Nov}, pages={784–796} }
 @article{bandara_mayorga_mclay_2014, title={Priority dispatching strategies for EMS systems}, volume={65}, ISSN={["1476-9360"]}, DOI={10.1057/jors.2013.95}, abstractNote={Emergency medical service (EMS) systems provide urgent medical care and transport. In this study we implement dispatching policies for EMS systems that incorporate the severity of the call in order to increase the survival probability of patients. A simulation model is developed to evaluate the performance of EMS systems. Performance is measured in terms of patients’ survival probability, since survival probability more directly mirrors patient outcomes. Different response strategies are evaluated utilizing several examples to study the nature of the optimal dispatching policy. The results show that dispatching the closest vehicle is not always optimal and dispatching vehicles considering priority of the call leads to an increase in the average survival probability of patients. A heuristic algorithm, that is easy to implement, is developed to dispatch ambulances for large-scale EMS systems. Computational examples show that the dispatching algorithm is valuable in increasing the patients’ survival probability.}, number={4}, journal={JOURNAL OF THE OPERATIONAL RESEARCH SOCIETY}, author={Bandara, Damitha and Mayorga, Maria E. and McLay, Laura A.}, year={2014}, month={Apr}, pages={572–587} }
 @article{sudtachat_mayorga_mclay_2014, title={Recommendations for dispatching emergency vehicles under multitiered response via simulation}, volume={21}, ISSN={["1475-3995"]}, DOI={10.1111/itor.12083}, abstractNote={Emergency medical service (EMS) systems provide medical care and transportation. While many real-world systems use multiple vehicle types to attend different call priorities, few guidelines exist about which vehicles to allocate in multitiered responses where more than one vehicle is sent per call. This paper makes recommendations for multiple-unit dispatch to multiple call priorities based on simulation optimization and heuristics. The objective is to maximize the overall expected survival probability of patients classified as “life-threatening”. We assume two types of medical units and three call priorities; and that information may be updated when the medical unit arrives on-scene. First, we study the optimal dispatching policies through several examples. Numerical results show that dispatching while considering call priorities, rather than dispatching the closest units, improves EMS system effectiveness. A heuristic algorithm is developed for large-scale problems. A comparison between the heuristic and closest policy is demonstrated using real-world data.}, number={4}, journal={INTERNATIONAL TRANSACTIONS IN OPERATIONAL RESEARCH}, author={Sudtachat, Kanchala and Mayorga, Maria E. and McLay, Laura A.}, year={2014}, month={Jul}, pages={581–617} }
 @article{chanta_mayorga_mclay_2014, title={The minimum p-envy location problem with requirement on minimum survival rate}, volume={74}, ISSN={["1879-0550"]}, DOI={10.1016/j.cie.2014.06.001}, abstractNote={In location problems for the public sector such as emergency medical service (EMS) systems, the issue of equity is an important factor for facility design. Several measures have been proposed to minimize inequity of a system. This paper considers an extension to the minimum p-envy location model by evaluating the objective of the model based on a survival function instead of on a distance function since survival probability is directly related to patient outcomes with a constraint on minimum survival rate. The model was tested on a real world data set from the EMS system at Hanover County, VA, and also compared to other location models. The results indicate that, not only does the enhanced p-envy model reduce inequity but we also find that more lives can be saved by using the survival function objective. A sensitivity analysis on different quality of service measures (survival probability and traveled distance) and different choices of priority assigned to serving facility is discussed.}, journal={COMPUTERS & INDUSTRIAL ENGINEERING}, author={Chanta, Sunarin and Mayorga, Maria E. and McLay, Laura A.}, year={2014}, month={Aug}, pages={228–239} }
 @article{mclay_mayorga_2013, title={A Dispatching Model for Server-to-Customer Systems That Balances Efficiency and Equity}, volume={15}, ISSN={1523-4614 1526-5498}, url={http://dx.doi.org/10.1287/msom.1120.0411}, DOI={10.1287/msom.1120.0411}, abstractNote={The decision about which servers to dispatch to which customers is an important aspect of service systems. This decision is complicated when servers must be equitably—as well as efficiently—dispatched to customers. In this paper, we formulate a model for determining how to optimally dispatch distinguishable servers to prioritized customers given a set of equity constraints. These issues are examined through the lens of emergency medical service (EMS) dispatch, for which a Markov decision process model is developed that captures how to dispatch ambulances (servers) to prioritized patients (customers). It is assumed that customers arrive sequentially, with the priority and location of each customer becoming known upon arrival. Four types of equity constraints are considered—two of which reflect customer equity and two of which reflect server equity—all of which draw upon the decision analytic and social science literature to compare the effects of different notions of equity on the resulting dispatching policies. The Markov decision processes are formulated as equity-constrained linear programming models. A computational example is applied to an EMS system to compare the different equity models.}, number={2}, journal={Manufacturing & Service Operations Management}, publisher={Institute for Operations Research and the Management Sciences (INFORMS)}, author={McLay, Laura A. and Mayorga, Maria E.}, year={2013}, month={May}, pages={205–220} }
 @article{mclay_mayorga_2013, title={A model for optimally dispatching ambulances to emergency calls with classification errors in patient priorities}, volume={45}, ISSN={0740-817X 1545-8830}, url={http://dx.doi.org/10.1080/0740817x.2012.665200}, DOI={10.1080/0740817x.2012.665200}, abstractNote={The decision of which servers to dispatch to which customers is an important aspect of service systems. Such decisions are complicated when servers have different operating characteristics, customers are prioritized, and there are errors in assessing customer priorities. This article formulates a model for determining how to optimally dispatch servers to prioritized customers given that dispatchers make classification errors in assessing the true customer priorities. These issues are examined through the lens of Emergency Medical Service (EMS) dispatch, for which a Markov Decision Process (MDP) model is developed that captures how to optimally dispatch ambulances (servers) to prioritized patients (customers). It is assumed that patients arrive sequentially, with the location and perceived priority of each patient becoming known upon arrival. The proposed model determines how to optimally dispatch ambulances to patients to maximize the long-run average utility of the system, defined as the expected coverag...}, number={1}, journal={IIE Transactions}, publisher={Informa UK Limited}, author={McLay, Laura A. and Mayorga, Maria E.}, year={2013}, month={Jan}, pages={1–24} }
 @article{mayorga_ahn_aydin_2013, title={Assortment and inventory decisions with multiple quality levels}, volume={211}, ISSN={0254-5330 1572-9338}, url={http://dx.doi.org/10.1007/s10479-013-1456-7}, DOI={10.1007/s10479-013-1456-7}, number={1}, journal={Annals of Operations Research}, publisher={Springer Science and Business Media LLC}, author={Mayorga, Maria E. and Ahn, Hyun-Soo and Aydin, Goker}, year={2013}, month={Sep}, pages={301–331} }
 @article{mayorga_bandara_mclay_2013, title={Districting and dispatching policies for emergency medical service systems to improve patient survival}, volume={3}, ISSN={1948-8300 1948-8319}, url={http://dx.doi.org/10.1080/19488300.2012.762437}, DOI={10.1080/19488300.2012.762437}, abstractNote={The major focus of Emergency Medical Service (EMS) system is to save lives and to minimize the effects of emergency health incidents. Districting, or designing pre-determined response areas, allows an EMS system to reduce the response time of paramedic support to the incident. Furthermore, dispatching policies affect system performance. Thus, in this study we propose integrated dispatching and districting policies to improve the performance of EMS systems. We measure performance in terms of patient survival probability. We propose several policies for districting/dispatching, these are provided as inputs to a simulation model that compares the performance of different policies. Our response areas, or districts, are designed using a constructive heuristic which considers adjusted expected coverage. Intra-district and inter-district dispatching policies are developed considering the degree of the urgency of the call. Computational results show that integrated districting and dispatching policies are vital i...}, number={1}, journal={IIE Transactions on Healthcare Systems Engineering}, publisher={Informa UK Limited}, author={Mayorga, Maria E. and Bandara, Damitha and McLay, Laura A.}, year={2013}, month={Jan}, pages={39–56} }
 @article{toro-díaz_mayorga_chanta_mclay_2013, title={Joint location and dispatching decisions for Emergency Medical Services}, volume={64}, ISSN={0360-8352}, url={http://dx.doi.org/10.1016/j.cie.2013.01.002}, DOI={10.1016/j.cie.2013.01.002}, abstractNote={The main purpose of Emergency Medical Service systems is to save lives by providing quick response to emergencies. The performance of these systems is affected by the location of the ambulances and their allocation to the customers. Previous literature has suggested that simultaneously making location and dispatching decisions could potentially improve some performance measures, such as response times. We developed a mathematical formulation that combines an integer programming model representing location and dispatching decisions, with a hypercube model representing the queuing elements and congestion phenomena. Dispatching decisions are modeled as a fixed priority list for each customer. Due to the model's complexity, we developed an optimization framework based on Genetic Algorithms. Our results show that minimization of response time and maximization of coverage can be achieved by the commonly used closest dispatching rule. In addition, solutions with minimum response time also yield good values of expected coverage. The optimization framework was able to consistently obtain the best solutions (compared to enumeration procedures), making it suitable to attempt the optimization of alternative optimization criteria. We illustrate the potential benefit of the joint approach by using a fairness performance indicator. We conclude that the joint approach can give insights of the implicit trade-offs between several conflicting optimization criteria.}, number={4}, journal={Computers & Industrial Engineering}, publisher={Elsevier BV}, author={Toro-Díaz, Hector and Mayorga, Maria E. and Chanta, Sunarin and McLay, Laura A.}, year={2013}, month={Apr}, pages={917–928} }
 @article{childers_mayorga_taaffe_2013, title={Prioritization strategies for patient evacuations}, volume={17}, ISSN={1386-9620 1572-9389}, url={http://dx.doi.org/10.1007/s10729-013-9236-0}, DOI={10.1007/s10729-013-9236-0}, number={1}, journal={Health Care Management Science}, publisher={Springer Science and Business Media LLC}, author={Childers, Ashley Kay and Mayorga, Maria E. and Taaffe, Kevin M.}, year={2013}, month={May}, pages={77–87} }
 @article{mayorga_reifsnider_neyens_gebregziabher_hunt_2013, title={Simulated estimates of pre-pregnancy and gestational diabetes mellitus in the US: 1980 to 2008}, volume={8}, DOI={10.1371/journal.pone.0073437}, abstractNote={To simulate national estimates of prepregnancy and gestational diabetes mellitus (GDM) in non-Hispanic white (NHW) and non-Hispanic black (NHB) women.Prepregnancy diabetes and GDM were estimated as a function of age, race/ethnicity, and body mass index (BMI) using South Carolina live singleton births from 2004-2008. Diabetes risk was applied to a simulated population. Age, natality and BMI were assigned to women according to race- and age-specific US Census, Natality and National Health and Nutrition Examination Surveys (NHANES) data, respectively.From 1980-2008, estimated GDM prevalence increased from 4.11% to 6.80% [2.68% (95% CI 2.58%-2.78%)] and from 3.96% to 6.43% [2.47% (95% CI 2.39%-2.55%)] in NHW and NHB women, respectively. In NHW women prepregnancy diabetes prevalence increased 0.90% (95% CI 0.85%-0.95%) from 0.95% in 1980 to 1.85% in 2008. In NHB women from 1980 through 2008 estimated prepregnancy diabetes prevalence increased 1.51% (95% CI 1.44%-1.57%), from 1.66% to 3.16%.Racial disparities in diabetes prevalence during pregnancy appear to stem from a higher prevalence of prepregnancy diabetes, but not GDM, in NHB than NHW.}, number={9}, journal={PLoS One}, author={Mayorga, Maria and Reifsnider, O. S. and Neyens, D. M. and Gebregziabher, M. G. and Hunt, K. J.}, year={2013} }
 @article{mcelreath_mayorga_2012, title={A dynamic programming approach to solving the assortment planning problem with multiple quality levels}, volume={39}, ISSN={0305-0548}, url={http://dx.doi.org/10.1016/j.cor.2011.08.023}, DOI={10.1016/j.cor.2011.08.023}, abstractNote={While the assortment planning problem, in which a firm selects a set of products to offer, has been widely studied, several problem instances exist which have not yet been solved to optimality. In particular, we consider an assortment planning problem under a locational choice model for consumer choice with both vertical and horizontal differentiation. We present a combined dynamic programming/line search approach which finds an optimal solution when customer preference for the horizontal attributes are distributed according to a unimodal distribution. The dynamic program makes use of new analytical results, which show that high quality products will be distributed near the mode. This enables significant state reduction and therefore efficient solution times. Efficient computation times allow us to study the solution for a wide range of system parameters and thereby draw several managerial conclusions.}, number={7}, journal={Computers & Operations Research}, publisher={Elsevier BV}, author={McElreath, Mark H. and Mayorga, Maria E.}, year={2012}, month={Jul}, pages={1521–1529} }
 @article{truong_reifsnider_mayorga_spitler_2012, title={Estimated Number of Preterm Births and Low Birth Weight Children Born in the United States Due to Maternal Binge Drinking}, volume={17}, ISSN={1092-7875 1573-6628}, url={http://dx.doi.org/10.1007/s10995-012-1048-1}, DOI={10.1007/s10995-012-1048-1}, abstractNote={The objective of this study was to estimate the aggregate burden of maternal binge drinking on preterm birth (PTB) and low birth weight (LBW) across American sociodemographic groups in 2008. To estimate the aggregate burden of maternal binge drinking on preterm birth (PTB) and low birth weight (LBW) across American sociodemographic groups in 2008. A simulation model was developed to estimate the number of PTB and LBW cases due to maternal binge drinking. Data inputs for the model included number of births and rates of preterm and LBW from the National Center for Health Statistics; female population by childbearing age groups from the U.S. Census; increased relative risks of preterm and LBW deliveries due to maternal binge drinking extracted from the literature; and adjusted prevalence of binge drinking among pregnant women estimated in a multivariate logistic regression model using Behavioral Risk Factor Surveillance System survey. The most conservative estimates attributed maternal binge drinking to 8,701 (95% CI: 7,804-9,598) PTBs (1.75% of all PTBs) and 5,627 (95% CI 5,121-6,133) LBW deliveries in 2008, with 3,708 (95% CI: 3,375-4,041) cases of both PTB and LBW. The estimated rate of PTB due to maternal binge drinking was 1.57% among all PTBs to White women, 0.69% among Black women, 3.31% among Hispanic women, and 2.35% among other races. Compared to other age groups, women ages 40-44 had the highest adjusted binge drinking rate and highest PTB rate due to maternal binge drinking (4.33%). Maternal binge drinking contributed significantly to PTB and LBW differentially across sociodemographic groups.}, number={4}, journal={Maternal and Child Health Journal}, publisher={Springer Science and Business Media LLC}, author={Truong, Khoa D. and Reifsnider, Odette S. and Mayorga, Maria E. and Spitler, Hugh}, year={2012}, month={Jun}, pages={677–688} }
 @article{hunt_marlow_gebregziabher_ellerbe_mauldin_mayorga_korte_2012, title={Impact of maternal diabetes on birthweight is greater in non-Hispanic blacks than in non-Hispanic whites}, volume={55}, ISSN={0012-186X 1432-0428}, url={http://dx.doi.org/10.1007/s00125-011-2430-z}, DOI={10.1007/s00125-011-2430-z}, abstractNote={To determine the impact of maternal diabetes during pregnancy on racial disparities in fetal growth.Using linked birth certificate, inpatient hospital and prenatal claims data we examined live singleton births of mothers resident in South Carolina who self-reported their race as non-Hispanic white (NHW; n = 140,128) or non-Hispanic black (NHB; n = 82,492) and delivered at 28-42 weeks' gestation between 2004 and 2008.Prepregnancy diabetes prevalence was higher in NHB (3.0%) than in NHW (1.7%), while the prevalence of gestational diabetes mellitus (GDM) was similar in NHB (6.1%) and NHW (6.3%). At a delivery BMI of 35 kg/m(2), GDM exposure was associated with an average birthweight only 17 g (95% CI 4, 30) higher in NHW, but 78 g (95% CI 61, 95) higher in NHB (controlling for gestational age, maternal age, infant sex and availability of information on prenatal care). Figures for prepregnancy diabetes were 58 g (95% CI 34, 81) in NHW and 60 g (95% CI 37, 84) in NHB. GDM had a greater impact on birthweight in NHB than in NHW (60 g racial difference [95% CI 39, 82]), while prepregnancy diabetes had a large but similar impact. Similarly, the RR for GDM of having a large- relative to a normal-weight-for-gestational-age infant was lower in NHW (RR 1.41 [95% CI 1.34, 1.49]) than in NHB (RR 2.24 [95% CI 2.05, 2.46]).These data suggest that the negative effects of GDM combined with obesity during pregnancy may be greater in NHB than in NHW individuals.}, number={4}, journal={Diabetologia}, publisher={Springer Science and Business Media LLC}, author={Hunt, K. J. and Marlow, N. M. and Gebregziabher, M. and Ellerbe, C. N. and Mauldin, J. and Mayorga, M. E. and Korte, J. E.}, year={2012}, month={Jan}, pages={971–980} }
 @article{hunt_alanis_johnson_mayorga_korte_2012, title={Maternal Pre-Pregnancy Weight and Gestational Weight Gain and Their Association with Birthweight with a Focus on Racial Differences}, volume={17}, ISSN={1092-7875 1573-6628}, url={http://dx.doi.org/10.1007/s10995-012-0950-x}, DOI={10.1007/s10995-012-0950-x}, abstractNote={Our objectives were to examine the interaction between maternal pre-pregnancy body mass index (BMI) and gestational weight gain (GWG) and their association with birthweight, with a focus on racial differences. We used birth certificate data from live singleton births of South Carolina resident mothers, who self-reported their race as non-Hispanic white (NHW, n = 140, 128) or non-Hispanic black (NHB, n = 82,492) and who delivered at 34-44 weeks of gestation between 2004 and 2008 to conduct a cross-sectional study. Linear regression was used to examine the relationship between our exposures (i.e., race, BMI and GWG) and our outcome birthweight. Based on 2009 Institute of Medicine guidelines, the prevalence of adequate, inadequate and excessive GWG was 27.1, 24.2 and 48.7%, respectively, in NHW women and 24.2, 34.8 and 41.0%, respectively, in NHB women. Adjusting for infant sex, gestational age, maternal age, tobacco use, education, prenatal care, and Medicaid, the difference in birthweight between excessive and adequate GWG at a maternal BMI of 30 kg/m(2) was 118 g (95% CI: 109, 127) in NHW women and 101 g (95% CI: 91, 111) in NHB women. Moreover, excessive versus adequate GWG conveyed similar protection from having a small for gestational age infant in NHW [OR = 0.64 (95% CI 0.61, 0.67)] and NHB women [OR = 0.68 (95% CI: 0.65, 0.72)]. In conclusion, we report a strong association between excessive GWG and higher infant birthweight across maternal BMI classes in NHW and NHB women. Given the high prevalence of excessive GWG even a small increase in birthweight may have considerable implications at the population level.}, number={1}, journal={Maternal and Child Health Journal}, publisher={Springer Science and Business Media LLC}, author={Hunt, Kelly J. and Alanis, Mark C. and Johnson, Erica R. and Mayorga, Maria E. and Korte, Jeffrey E.}, year={2012}, month={Feb}, pages={85–94} }
 @inbook{leclerc_mclay_mayorga_2012, place={New York}, edition={1}, series={International Series in Operations Research & Management Science}, title={Modeling equity for allocation in public resources}, booktitle={Community-Based Operations Research: Decision Modeling for Local Impact and Diverse Populations}, publisher={Springer}, author={Leclerc, P.D. and McLay, L.A. and Mayorga, M.E.}, editor={Johnson, M.Editor}, year={2012}, pages={97–118}, collection={International Series in Operations Research & Management Science} }
 @article{bandara_mayorga_mclay_2012, title={Optimal dispatching strategies for emergency vehicles to increase patient survivability}, volume={15}, ISSN={1745-7645 1745-7653}, url={http://dx.doi.org/10.1504/ijor.2012.048867}, DOI={10.1504/ijor.2012.048867}, abstractNote={A major focus of emergency medical service (EMS) systems is to save lives and to minimise the effect of an emergency health incident. The objective of this research is to determine how to optimally dispatch paramedic units to emergency calls to maximise patients’ survivability. We formulate the problem as Markov decision process to obtain the optimal dispatching policies. These dispatching policies are developed incorporating the degree of the urgency of the call. The optimal policy provides an ordered preference (priority) list of ambulances to dispatch. The performance of the proposed dispatching rules is evaluated in terms of patients’ survivability rather than measuring the response time thresholds, as survival probability more directly mirrors patient outcomes. Computational examples show that dispatching the closest vehicle is not always optimal and that dispatching vehicles considering the priority of the call leads to an increase in the average survival probability of patients.}, number={2}, journal={International Journal of Operational Research}, publisher={Inderscience Publishers}, author={Bandara, Damitha and Mayorga, Maria E. and McLay, Laura A.}, year={2012}, pages={195} }
 @article{bhattacharyya_mayorga_melloy_2011, title={A Phenomenographic Analysis of Three Real-World Experiences in Clemson University’s Industrial Engineering Program}, journal={Journal of Applications and Practices in Engineering Education}, author={Bhattacharyya, G. and Mayorga, M.E. and Melloy, B.}, year={2011} }
 @article{mclay_mayorga_2011, title={Evaluating the impact of performance goals on dispatching decisions in emergency medical service}, volume={1}, ISSN={1948-8300 1948-8319}, url={http://dx.doi.org/10.1080/19488300.2011.618820}, DOI={10.1080/19488300.2011.618820}, abstractNote={Most emergency medical service systems measure performance based on the coverage level for a given response time threshold, i.e., the proportion of 911 calls responded to within a fixed timeframe. The ultimate goal of emergency medical service systems is to save lives, which suggests that it might be worthwhile to consider using performance measures more closely tied to patient outcomes. This paper examines how the goal of maximizing coverage for different response time thresholds impacts patient survival rates in the context of emergency medical dispatch. Results illustrated using real-world data from Hanover County, Virginia indicate that dispatching ambulances to maximize an eight minute response time threshold simultaneously maximizes patient survival. A sensitivity analysis over different ambulance location configurations and call arrival rates confirms that seven and eight minute response time thresholds are robust. These results corroborate previous results that consider the decision context of loc...}, number={3}, journal={IIE Transactions on Healthcare Systems Engineering}, publisher={Informa UK Limited}, author={McLay, Laura A. and Mayorga, Maria E.}, year={2011}, month={Jul}, pages={185–196} }
 @article{mayorga_ahn_2011, title={Joint management of capacity and inventory in make-to-stock production systems with multi-class demand}, volume={212}, ISSN={0377-2217}, url={http://dx.doi.org/10.1016/j.ejor.2011.01.047}, DOI={10.1016/j.ejor.2011.01.047}, abstractNote={We evaluate the benefits of coordinating capacity and inventory decisions in a make-to-stock production environment. We consider a firm that faces multi-class demand and has additional capacity options that are temporary and randomly available. We formulate the model as a Markov decision process (MDP) and prove that a solution to the optimal joint control problem exists. For several special cases we characterize the structure of the optimal policy. For the general case, however, we show that the optimal policy is state-dependent, and in many instances non-monotone and difficult to implement. Therefore, we consider three pragmatic heuristic policies and assess their performance. We show that the majority of the savings originate from the ability to dynamically adjust capacity, and that a simple heuristic that can adjust production capacity (based on workload fluctuation) but uses a static production/rationing policy can result in significant savings.}, number={2}, journal={European Journal of Operational Research}, publisher={Elsevier BV}, author={Mayorga, Maria E. and Ahn, Hyun-Soo}, year={2011}, month={Jul}, pages={312–324} }
 @article{chanta_mayorga_kurz_mclay_2011, title={The minimump-envy location problem: a new model for equitable distribution of emergency resources}, volume={1}, ISSN={1948-8300 1948-8319}, url={http://dx.doi.org/10.1080/19488300.2011.609522}, DOI={10.1080/19488300.2011.609522}, abstractNote={Equity is an important consideration in public services such as Emergency Medical Service (EMS) systems. In such systems not only equitability but also performance depends on the spatial distribution of facilities and resources. This paper proposes the minimum p-envy facility location model which aims to find optimal locations for facilities in order to balance customers’ perceptions of equity in receiving service. The model is developed and evaluated through the lens of EMS systems, where ambulances are located at facilities (stations) with the objective of minimizing the sum of “envy” among all demand zones (customer points) with respect to an ordered set of p operating stations weighted by the proportion of demand in each zone. The problem is formulated as an integer program, with priority weights assigned according the probability that an ambulance is available, which is estimated using the hypercube model. Because of the computational effort required to obtain solutions using commercially available s...}, number={2}, journal={IIE Transactions on Healthcare Systems Engineering}, publisher={Informa UK Limited}, author={Chanta, Sunarin and Mayorga, Maria E. and Kurz, Mary E. and McLay, Laura A.}, year={2011}, month={Apr}, pages={101–115} }
 @article{mayorga_subramanian_2010, title={Factoring environmental concerns in supply chain decision making}, volume={4}, ISSN={1751-200X 1751-2018}, url={http://dx.doi.org/10.1504/ijbsr.2010.033424}, DOI={10.1504/ijbsr.2010.033424}, abstractNote={Recent regulatory and market-driven environmental pressures have fundamentally impacted decision making throughout supply chain systems, from raw material sourcing through processing, use and post-use – including the logistical activities in between. In this paper, we focus on three factors – legislative, economic and social – that have introduced environment-related complexities into supply chain decisions. For each of these factors, we provide examples of how the accompanying complexities can be characterised within decision models in the form of parameters, objectives or constraints. The contribution of this work lies in highlighting that conventional supply chain decision models have to be recast and solved differently to accommodate legislative, economic and social pressures related to the life-cycle environmental impacts of products or technologies.}, number={4}, journal={International Journal of Business and Systems Research}, publisher={Inderscience Publishers}, author={Mayorga, Maria E. and Subramanian, Ravi}, year={2010}, pages={469} }
 @article{mcelreath_mayorga_kurz_2010, title={Metaheuristics for assortment problems with multiple quality levels}, volume={37}, ISSN={0305-0548}, url={http://dx.doi.org/10.1016/j.cor.2010.01.011}, DOI={10.1016/j.cor.2010.01.011}, abstractNote={The assortment planning problem involves choosing an optimal product line, as defined by a set of products with specific attributes, to offer consumers. Under a locational choice model in which products are differentiated both horizontally (by variety attributes) and vertically (by quality attributes), an optimal assortment, whose attributes have only been partially characterized, may consist of multiple quality levels. Using previous analytical results, we approximate the optimal assortment for make-to-order and static substitution environments. We test the appropriateness and compare the performance of three metaheuristic methods. These metaheuristics can easily be modified to accommodate different consumer preference distribution assumptions.}, number={10}, journal={Computers & Operations Research}, publisher={Elsevier BV}, author={McElreath, Mark H. and Mayorga, Maria E. and Kurz, Mary E.}, year={2010}, month={Oct}, pages={1797–1804} }
 @article{mcdonnell_mayorga_benson_mears_2010, title={Stepping Out of Academics: The Effect of Authentic Learning Experiences on Attitudes of IE Students}, volume={1}, number={2}, journal={Journal of Applications and Practices in Engineering Education}, author={McDonnell, D. and Mayorga, M.E. and Benson, L. and Mears, L.}, year={2010} }
 @article{mayorga_taaffe_arumugam_2009, title={Allocating flexible servers in serial systems with switching costs}, volume={172}, ISSN={0254-5330 1572-9338}, url={http://dx.doi.org/10.1007/s10479-009-0575-7}, DOI={10.1007/s10479-009-0575-7}, number={1}, journal={Annals of Operations Research}, publisher={Springer Science and Business Media LLC}, author={Mayorga, Maria E. and Taaffe, Kevin M. and Arumugam, Ramesh}, year={2009}, month={May}, pages={231–242} }
 @article{mclay_mayorga_2009, title={Evaluating emergency medical service performance measures}, volume={13}, ISSN={1386-9620 1572-9389}, url={http://dx.doi.org/10.1007/s10729-009-9115-x}, DOI={10.1007/s10729-009-9115-x}, number={2}, journal={Health Care Management Science}, publisher={Springer Science and Business Media LLC}, author={McLay, Laura A. and Mayorga, Maria E.}, year={2009}, month={Aug}, pages={124–136} }
 @inbook{mayorga_subramanian_2009, title={Incorporating Environmental Concerns in Supply Chain Optimization}, ISBN={9780470432730 9780470170700}, url={http://dx.doi.org/10.1002/9780470432730.ch4}, DOI={10.1002/9780470432730.ch4}, booktitle={Environmentally Conscious Materials Handling}, publisher={John Wiley & Sons, Inc.}, author={Mayorga, Maria E. and Subramanian, Ravi}, year={2009}, month={Jul}, pages={117–135} }
 @article{arumugam_mayorga_taaffe_2008, title={Inventory based allocation policies for flexible servers in serial systems}, volume={172}, ISSN={0254-5330 1572-9338}, url={http://dx.doi.org/10.1007/s10479-008-0465-4}, DOI={10.1007/s10479-008-0465-4}, number={1}, journal={Annals of Operations Research}, publisher={Springer Science and Business Media LLC}, author={Arumugam, Ramesh and Mayorga, Maria E. and Taaffe, Kevin M.}, year={2008}, month={Nov}, pages={1–23} }
 @article{mayorga_ahn_shanthikumar_2006, title={Optimal control of a make-to-stock system with adjustable service rate}, volume={20}, ISSN={0269-9648 1469-8951}, url={http://dx.doi.org/10.1017/s0269964806060384}, DOI={10.1017/s0269964806060384}, abstractNote={We consider a multiclass make-to-stock system served by a single server with adjustable capacity (service rate). At any point in time, the decision-maker must determine the capacity level, make a production decision (i.e., whether to produce an item to stock or to satisfy a backorder), and make a rationing decision (i.e., whether to satisfy a new order from stock or place it on backorder). In this article we characterize the structure of optimal capacity adjustment, production, and stock rationing policy for both finite- and infinite-horizon problems. We show that an optimal policy is monotone in current inventory and backorder levels, and we characterize its properties. In a numerical study we compare the optimal policy with heuristic policies and show that the savings from using an optimal policy can be significant.}, number={4}, journal={Probability in the Engineering and Informational Sciences}, publisher={Cambridge University Press (CUP)}, author={Mayorga, Maria E. and Ahn, Hyun-Soo and Shanthikumar, J. George}, year={2006}, month={Sep}, pages={609–634} }