A note on the sample size determination in two-period repeated measurements crossover design with application to clinical trials.

The two-period repeated measurements crossover design is often used in clinical trials. In this article we give a formula for sample size determination for testing treatment effect in two-period repeated measurements crossover design by taking an analysis of variance approach to the repeated measurements analysis. A balanced situation is considered: two treatment sequences that have the same number of patients, and the time points of measurements on each subject within each treatment period equal in number. The formula reveals the relationship between the required number of patients for each treatment sequence, the number of repeated measurements within each treatment period, the detectable treatment difference with respect to a primary response variable, and the power for testing the treatment difference. A clinical trial example is given to illustrate the use of the formula.