Faculty and students are involved in a number of collaborative research projects in the biomedical and behavioral sciences, including bioinformatics (see above) of inherited diseases, neuroscience (see below), and the design and analysis of clinical studies. An underlying theme in our work is the use of statistical methods to better understand heterogeneity in study populations. Traditional statistical models attempt to explain the mean response of each individual in the study. Frequently, however, this is not possible because key variables may not be directly observable. For example, genetic differences among patients may lead them to respond differently to a drug therapy. We are also interested in methods for generating and evaluating evidence about what treatments work for whom and under what conditions through combining information generated from different study designs, such as randomized controlled trials, epidemiological studies, and administrative databases. While sometimes we lead the fundamental scientific work, often we collaborate with investigators at the University of Pittsburgh Medical Center and/or with others worldwide.