We illustrate nonparametric, and particularly rank-based analyses of crossover studies, designs in which each subject receives more than one treatment over time. Principles involved in using the Wilcoxon rank sum test in the simple two-period, two-treatment crossover are described through theory and example. We then extend the ideas to two-treatment designs with more than two periods and to three-treatment, three-period designs. When more than one nonparametric approach is available, we consider the issue of statistical power in choosing an appropriate test.
"Nonparametric Approaches to the Analysis of Crossover Studies." Statist. Sci. 19 (4) 712 - 719, November 2004. https://doi.org/10.1214/088342304000000611