Non-Parametric Methods

Published article describing the non-parametric methods most commonly used in medical research.

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What this resource offers

This article gives a concise description of some simple non-parametric methods that are commonly used in medical research and their strengths and limitations. It describes in detail three of the most common methods: the sign test, the Wilcoxon signed rank test, and the Wilcoxon rank sum (or Mann-Whitney) test.


Elise Whitley and Jonathan Ball (2002), “Statistics review 6: Nonparametric methods”, Critical Care 6(6), 509–513.

Who created it

Elise Whitley, Lecturer in Medical Statistics, University of Bristol, Bristol, UK, and Jonathan Ball, Lecturer in Intensive Care Medicine, St George's Hospital Medical School, London, UK. This article is the sixth in an educational review series on medical statistics, in the journal Critical Care.