This book focuses on the rationale of choosing the noninferiority (NI) margin as a small fraction of the therapeutic effect of the active control in a clinical trial. It discusses issues of estimating the effect size based on historical placebo control trials of the active control. The book also covers basic concepts related to NI trials, such as essay sensitivity, constancy assumption, discounting, and preservation. Other topics described include patient populations, three-arm trials, and testing equivalence of three or more groups--Provided by publisher.