Equivalence trials have the objective of demonstrating that an investigational treatment, for example, a test drug under development, is not different from a reference treatment by more than a prespecified clinically irrelevant amount. The purpose of this paper is to investigate for the crossover design the situation when equivalence is defined in terms of the ratio of location parameters. An approximate formula for sample size calculation is presented for the case of normally distributed endpoints, and nonparametric methods for testing and calculation of confidence intervals are provided.
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