This article describes how to perform the Wilcoxon rank-sum test to compare the median between two samples.
This test can be applied to two samples of equal or different sizes. For paired samples see Test - Nonparametric - Paired Samples Wilcoxon Test.
A Displayr document with a data set.
- Go to Anything > Advanced Analysis > Test > Nonparametric > Two Sample Wilcoxon Rank Sum Test.
- Specify the outcome variable to use under Inputs > Two-Sample Wilcoxon Test > Outcome. The outcome variable is the variable containing the sample to analyze.
- Under Inputs > Two-Sample Wilcoxon Test > Group, specify the variable that each observation comes from. Where this variable is numeric, it is automatically grouped into two approximately equally sized groups, using the median, and will be automatically converted by the function.
OPTIONAL: You can modify the following settings to adjust the output:
- mu - Difference in the median of the two samples, as assumed under the null hypothesis.
- Alternative hypothesis - Use a two-sided or one-sided test.
- Type of test - Method by which the p-value is computed.
- Summary - Shows a nicely formatted table of the test results (default).
- R - The original text-based output from the wilcox.test function.
- Variable names - Display Variable Names in the output, instead of Variable Labels.
- More decimal places - Display numeric values with 8 decimal places.