Considerations for crossover design in clinical study

This article introduces a crossover design that is often used in clinical studies, with the ad-vantage of comparing treatment effects within one study subject. In particular, the advan-tages and disadvantages of the two-period, two-sequence crossover design (2 × 2 or AB/ BA crossover design), which is widely used in clinical practice, are identified, and the ele-ments necessary for analysis are introduced. This article explains the carryover effect, period effect, sequence effect, and period-by-treatment interaction in a crossover design and examines the analysis commands of SAS along with example data. After confirming the carryover effect using a general linear model, the treatment effect is analyzed using a linear mixed effect model.