Wilcoxon rank-sum test
Topic of Estimation examples, part of Data analysis
Wilcoxon rank-sum test
| Type | Topic |
| Taught in | Estimation examples |
| Part | Data analysis |
A test for a shift between two independent samples that uses only the ranks of the pooled observations, so it does not need normality. It is the safer choice than a two-sample t procedure for small, skewed samples.
In Estimation examples
From Estimation examples
The effective degrees of freedom lie between the smaller of n_1-1 and n_2-1 and the pooled n_1+n_2-2. For non-normal data the interval is still approximately right when both samples are reasonably large, say 30 or more; for small, skewed samples a rank-based method such as the Wilcoxon rank-sum test is safer.
Used in
See also
Skewness · Margin of error · Welch interval · From data to an estimate · Large-sample intervals · Small normal samples · Two samples with unequal variances · Intervals for proportions