Home  >>  Archives  >>  Volume 13 Number 2  >>  st0297

The Stata Journal
Volume 13 Number 2: pp. 337-343



Subscribe to the Stata Journal
cover

Exact Wilcoxon signed-rank and Wilcoxon Mann-Whitney ranksum tests

Tammy Harris
Institute for Families in Society
Department of Epidemiology & Biostatistics
University of South Carolina
Columbia, SC
harris68@mailbox.sc.edu
James W. Hardin
Institute for Families in Society
Department of Epidemiology
& Biostatistics
University of South Carolina
Columbia, SC
jhardin@sc.edu
Abstract.  We present new Stata commands for carrying out exact Wilcoxon one-sample and two-sample comparisons of the median. Nonparametric tests are often used in clinical trials, in which it is not uncommon to have small samples. In such situations, researchers are accustomed to making inferences by using exact statistics. The ranksum and signrank commands in Stata provide only asymptotic results, which assume normality. Because large-sample results are unacceptable in many clinical trials studies, these researchers must use other software packages. To address this, we have developed new commands for Stata that provide exact statistics in small samples. Additionally, when samples are large, we provide results based on the Student’s t distribution that outperform those based on the normal distribution.
Buy article (PDF): $11.75 View cart
Buy entire issue (PDF): $24.75

View all articles by these authors: Tammy Harris, James W. Hardin

View all articles with these keywords: ranksumex, signrankex, exact distributions, nonparametric tests, median, Wilcoxon matched-pairs signed-rank test, Wilcoxon ranksum test

Download citation: BibTeX  RIS

Download citation and abstract: BibTeX  RIS