| Abstract: | The Wilcoxon–Mann–Whitney (WMW) test is the most commonly used nonparametric method to compare two treatments when the underlying distribution of the outcome variable is not normally distributed. The sample size calculation methods for the WMW test have been extensively discussed in the literature. In this article we give a comprehensive review of sample size calculation methods for the WMW test on data with or without ties. We also provide detailed implementation of these sample size calculation methods for the WMW test depending on the characteristics of the data and the amount of available information. In addition, the implementation of these methods in popular sample size calculation software packages is also discussed. This article will be very helpful for researchers to determine sample sizes for the WMW test in the design phase of a study. |
