The first specific aim of this proposal is to train the applicant in the biostatistical aspects of the design, conduct, and analysis of multi-center clinical trials. This will be achieved by the applicant's participation in the sponsor's data coordinating center activities for two large networks funded by the National Heart, Lung, and Blood Institute, namely, the Asthma Clinical Research Network (ACRN) and the Childhood Asthma Research and Education (CARE) Network.. In addition, the applicant will undertake formal instruction via the sponsoring department's course offerings in biostatistics, clinical trials, and statistical genetics. The second specific aim is to investigate the biostatistical properties of more complex models for carryover effects in crossover designs, which are commonly used in clinical trials with a chronic disease.