# In what situations should the Wilcoxon rank sum test be used rather than the independent samples t test?

## In what situations should the Wilcoxon rank sum test be used rather than the independent samples t test?

The Wilcoxon Rank Sum Test is often described as the non-parametric version of the two-sample t-test. You sometimes see it in analysis flowcharts after a question such as “is your data normal?” A “no” branch off this question will recommend a Wilcoxon test if you’re comparing two groups of continuous measures.

### What does a Wilcoxon rank sum test tell you?

The Wilcoxon test is a nonparametric statistical test that compares two paired groups, and comes in two versions the Rank Sum test or the Signed Rank test. The goal of the test is to determine if two or more sets of pairs are different from one another in a statistically significant manner.

When should you use the Wilcoxon rank sum test?

The Wilcoxon rank-sum test is commonly used for the comparison of two groups of nonparametric (interval or not normally distributed) data, such as those which are not measured exactly but rather as falling within certain limits (e.g., how many animals died during each hour of an acute study).

Does the Wilcoxon test compare medians?

The wilcox. test( ) function will perform the Wilcoxon signed rank test comparing medians for paired samples. The paired data must be represented by two data vectors with the same number of subjects.

## Is t-test better than Wilcoxon?

Fulfillment of assumptions: The assumptions of Student’s t-test may not be met for small sample sizes. In this case, it is often safer to select a non-parametric test. However, if the assumptions of the t-test are met, it has greater statistical power than Wilcoxon’s test.

### What must you include when applying Wilcoxon rank-sum test?

Generally speaking, for the Wilcoxon Rank-Sum Test to be valid, the X and Y samples must be independent, and X and Y must be continuous random variables.

What is the difference between the Wilcoxon rank sum test and Wilcoxon signed-rank test?

Wilcoxon rank-sum test is used to compare two independent samples, while Wilcoxon signed-rank test is used to compare two related samples, matched samples, or to conduct a paired difference test of repeated measurements on a single sample to assess whether their population mean ranks differ.

Is Wilcoxon a t-test?

When applied to test the location of a set of samples, it serves the same purpose as the one-sample Student’s t-test. On a set of matched samples, it is a paired difference test like the paired Student’s t-test (also known as the “t-test for matched pairs” or “t-test for dependent samples”).