My research focuses are on the development of statistical methodologies in clinical trials of all phases. They include, but are not limited to, sample size estimation for longitudinal trials, evaluation of large number of non-inferiority trials, detection of qualitative interaction in the equivalence trials, analysis of count data in various vaccine trials, survival model with random effect for cancer studies, multivariate survival model, analysis of non-ignorable missing data in longitudinal trials, and statistical issues arising from the regulatory submission of NDA or BLA, etc.