@article{oberg_davidian_2000, title={Estimating data transformations in nonlinear mixed effects models}, volume={56}, ISSN={["0006-341X"]}, DOI={10.1111/j.0006-341X.2000.00065.x}, abstractNote={Summary.  A routine practice in the analysis of repeated measurement data is to represent individual responses by a mixed effects model on some transformed scale. For example, for pharmacokinetic, growth, and other data, both the response and the regression model are typically transformed to achieve approximate within‐individual normality and constant variance on the new scale; however, the choice of transformation is often made subjectively or by default, with adoption of a standard choice such as the log. We propose a mixed effects framework based on the transform‐both‐sides model, where the transformation is represented by a monotone parametric function and is estimated from the data. For this model, we describe a practical fitting strategy based on approximation of the marginal likelihood. Inference is complicated by the fact that estimation of the transformation requires modification of the usual standard errors for estimators of fixed effects; however, we show that, under conditions relevant to common applications, this complication is asymptotically negligible, allowing straightforward implementation via standard software.}, number={1}, journal={BIOMETRICS}, author={Oberg, A and Davidian, M}, year={2000}, month={Mar}, pages={65–72} }
 @article{oberg_ferguson_mcintyre_horner_2000, title={Incidence of stroke and season of the year: Evidence of an association}, volume={152}, ISSN={["1476-6256"]}, DOI={10.1093/aje/152.6.558}, abstractNote={Evidence of seasonal variation in the incidence of stroke is inconsistent. This may be a likely consequence of one or more methodological shortcomings of the studies investigating this issue, including inappropriate analytic models, insufficient length of time, small sample size, and a regional (vs. national) focus. The authors' objective was to ascertain whether an association exists between season of the year and the incidence of stroke by using a methodological approach designed to overcome these limitations. The authors used a longitudinal study design involving 72,779 veterans hospitalized for stroke at any Veterans Affairs hospital nationally during the years 1986-1995. These data were analyzed by using time series methods. There was clear evidence of a seasonal occurrence for stroke in general. This seasonal effect was found for ischemic stroke, but not for hemorrhagic stroke. The peak occurrence was in mid-May. Neither the region (i.e., climate) nor the race of the patient substantially modified the seasonal trend. An explanation for this pattern remains to be determined.}, number={6}, journal={AMERICAN JOURNAL OF EPIDEMIOLOGY}, author={Oberg, AL and Ferguson, JA and McIntyre, LM and Horner, RD}, year={2000}, month={Sep}, pages={558–564} }