On power and sample size determinations for the Wilcoxon-Mann-Whitney test

Gwowen Shieh, Show Li Jan, Ronald H. Randles*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

17 Scopus citations


This article considers power and sample size calculations for the Wilcoxon-Mann-Whitney test. An exact variance large-sample method is introduced and explicit formulas are derived for the uniform, normal, double exponential and exponential shift models. A Monte Carlo simulation study is conducted to evaluate the exact variance procedure and compare its performance with some other large sample methods. The results show the remarkable accuracy of the suggested formula and the fundamental limitations of the other approximations. Practical considerations in determination of sample size for the two-sample location problem are also discussed.

Original languageEnglish
Pages (from-to)33-43
Number of pages11
JournalJournal of Nonparametric Statistics
Issue number1
StatePublished - 1 Jan 2006


  • Large-sample approximation
  • Nonparametric method
  • Two-sample location problem

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