@article{johansson_whitaker_hagler_bowman_slate_payne_2006, title={Predicting aflatoxin and fumonisin in shelled corn lots sing poor-quality grade components}, volume={89}, number={2}, journal={Journal of AOAC International}, author={Johansson, A. S. and Whitaker, T. B. and Hagler, W. M. and Bowman, D. T. and Slate, A. B. and Payne, G.}, year={2006}, pages={433–440} }
@article{whitaker_johansson_2005, title={Sampling uncertainties for the detection of chemical agents in complex food matrices}, volume={68}, ISSN={["1944-9097"]}, DOI={10.4315/0362-028X-68.6.1306}, abstractNote={Using uncertainty associated with detection of aflatoxin in shelled corn as a model, the uncertainty associated with detecting chemical agents intentionally added to food products was evaluated. Accuracy and precision are two types of uncertainties generally associated with sampling plans. Sources of variability that affect precision were the primary focus of this investigation. Test procedures used to detect chemical agents generally include sampling, sample preparation, and analytical steps. The uncertainty of each step contributes to the total uncertainty of the test procedure. Using variance as a statistical measure of uncertainty, the variance associated with each step of the test procedure used to detect aflatoxin in shelled corn was determined for both low and high levels of contamination. For example, when using a 1-kg sample, Romer mill, 50-g subsample, and high-performance liquid chromatography to test a lot of shelled corn contaminated with aflatoxin at 10 ng/g, the total variance associated with the test procedure was 149.2 (coefficient of variation of 122.1%). The sampling, sample preparation, and analytical steps accounted for 83.0, 15.6, and 1.4% of the total variance, respectively. A variance of 149.2 suggests that repeated test results will vary from 0 to 33.9 ng/g. Using the same test procedure to detect aflatoxin at 10,000 ng/g, the total variance was 264,719 (coefficient of variation of 5.1%). The sampling, sample preparation, and analytical steps accounted for 41, 57, and 2% of the total variance, respectively. A variance of 264,719 suggests that repeated test results will vary from 8,992 to 11,008 ng/g. Foods contaminated at low levels reflect a situation in which a small percentage of particles is contaminated and sampling becomes the largest source of uncertainty. Large samples are required to overcome the "needle-in-the-haystack" problem. Aflatoxin is easier to detect and identify in foods intentionally contaminated at high levels than in foods with low levels of contamination because the relative standard deviation (coefficient of variation) decreases and the percentage of contaminated kernels increases with an increase in concentration.}, number={6}, journal={JOURNAL OF FOOD PROTECTION}, author={Whitaker, TB and Johansson, AS}, year={2005}, month={Jun}, pages={1306–1313} }
@article{whitaker_hagler_giesbrecht_johansson_2002, title={Sampling wheat for deoxynivalenol}, ISBN={0306467801}, DOI={10.1007/978-1-4615-0629-4_8}, abstractNote={The variability associated with testing wheat for deoxynivalenol (DON) was measured using a 0.454 kg sample, a Romer mill, 25 g of comminuted subsample and the Romer Fluoroquant analytical method. The total variability was partitioned into sampling, sample preparation, and analytical variability components. Each variance component was found to be a function of the DON concentration and equations were developed to predict each variance component using regression techniques. The effects of sample size, subsample size, and number of aliquots on reducing the variability of the DON test procedure were also determined. Using the test procedure described above, the coefficient of variation (CV) associated with testing wheat at 5 ppm DON was found to be 13.4%. The CVs associated with sampling, sample preparation, and analysis were 6.3, 10.0, and 6.3%, respectively. The sample variations associated with testing wheat are relatively small when compared to CVs associated with testing other commodities for other mycotoxins such as aflatoxin in peanuts. Even with the use of a small sample size (0.454 kg), the sampling variation was not the largest source of error as found in other mycotoxin test procedures.}, journal={Mycotoxins and food safety (Advances in experimental medicine and biology; v. 504)}, publisher={New York: Kluwer Academic/Plenum Publishers}, author={Whitaker, T. B. and Hagler, W. M. and Giesbrecht, F. G. and Johansson, A. S.}, editor={J. W. DeVries, M. W. Trucksess and Jackson, L. S.Editors}, year={2002}, pages={73–83} }
@article{whitaker_hagler_johansson_giesbrecht_trucksess_2001, title={Distribution among sample test results when testing shelled corn lots for fumonisin}, volume={84}, number={3}, journal={Journal of AOAC International}, author={Whitaker, T. B. and Hagler, W. M. and Johansson, A. S. and Giesbrecht, F. G. and Trucksess, M. W.}, year={2001}, pages={770–776} }
@article{whitaker_wu_peterson_giesbrecht_johansson_2001, title={Variability associated with the official USDA sampling plan used to inspect export wheat shipments for Tilletia controversa spores}, volume={50}, ISSN={["1365-3059"]}, DOI={10.1046/j.1365-3059.2001.00640.x}, abstractNote={The variability associated with estimating the true concentration of teliospores of dwarf bunt (Tilletia controversa) per 50 g of wheat (TC concentration) in an export wheat shipment was studied by measuring the TC concentration in 16 test samples (50 g) taken from each of 137 export shipments. The variability among the 16 TC test sample results, as measured by the standard deviation, was found to increase with TC concentration. The functional relationship was approximately linear in a full‐log plot and regression analysis was used to determine the coefficients of the regression equation. Using statistical theory, the regression equation was modified to predict the standard deviation among test sample sizes other than the 50 g size used in this study. The standard deviation and coefficient of variation associated with using a 50 g test sample to estimate the true TC concentration of a wheat shipment with 2000 spores per 50 g were estimated to be 1062·8 and 53·1%, respectively. Increasing test sample size to 1600 g reduced the standard deviation and coefficient of variation to 187·9 and 9·4%, respectively.}, number={6}, journal={PLANT PATHOLOGY}, author={Whitaker, TB and Wu, J and Peterson, GL and Giesbrecht, FG and Johansson, AS}, year={2001}, month={Dec}, pages={755–760} }
@article{whitaker_hagler_giesbrecht_johansson_2000, title={Sampling, sample preparation, and analytical variability associated with testing wheat for deoxynivalenol}, volume={83}, number={5}, journal={Journal of AOAC International}, author={Whitaker, T. B. and Hagler, W. M. and Giesbrecht, F. G. and Johansson, A. S.}, year={2000}, pages={1285–1292} }
@article{johansson_whitaker_hagler_giesbrecht_young_bowman_2000, title={Testing shelled corn for aflatoxin, Part I: Estimation of variance components}, volume={83}, number={5}, journal={Journal of AOAC International}, author={Johansson, A. S. and Whitaker, T. B. and Hagler, W. M. and Giesbrecht, F. G. and Young, J. H. and Bowman, D. T.}, year={2000}, pages={1264–1269} }
@article{johansson_whitaker_giesbrecht_hagler_young_2000, title={Testing shelled corn for aflatoxin, Part II: Modeling the observed distribution of aflatoxin test results}, volume={83}, number={5}, journal={Journal of AOAC International}, author={Johansson, A. S. and Whitaker, T. B. and Giesbrecht, F. G. and Hagler, W. M. and Young, J. H.}, year={2000}, pages={1270–1278} }
@article{johansson_whitaker_giesbrecht_hagler_young_2000, title={Testing shelled corn for aflatoxin, Part III: Evaluating the performance of aflatoxin sampling plans}, volume={83}, number={5}, journal={Journal of AOAC International}, author={Johansson, A. S. and Whitaker, T. B. and Giesbrecht, F. G. and Hagler, W. M. and Young, J. H.}, year={2000}, pages={1279–1284} }
@article{whitaker_trucksess_johansson_giesbrecht_hagler_bowman_1998, title={Variability associated with testing shelled corn for fumonisin}, volume={81}, number={6}, journal={Journal of AOAC International}, author={Whitaker, T. B. and Trucksess, M. W. and Johansson, A. S. and Giesbrecht, F. G. and Hagler, W. M. and Bowman, D. T.}, year={1998}, pages={1162–1168} }