Analysis of a crossover clinical trial by permutation methods

An initially balanced crossover design is analyzed by permutation rather than parametric methods in order to obtain exact distribution-free significance levels, thus controlling type I error and increasing power. The analysis is first restricted to those subjects who completed all nine periods. Next, it is extended to those who successfully completed two of the three blocks of treatments or six periods. Finally, we show how these distribution-free results may be extended to any number of treatment sequences and treatments in a balanced crossover design.