Mann-Whitney U Test Calculator
This calculator performs the Mann-Whitney U test (also called Wilcoxon rank-sum test), a non-parametric alternative to the independent samples t-test. Use this when your data doesn't meet the normality assumption.
The calculator offers exact permutation and approximate p-values. Exact inference assumes observations are exchangeable under the null hypothesis and supports tied ranks. It enumerates up to 200,000 group assignments; automatic mode uses the tie-corrected normal approximation above that limit. The result identifies the method actually used.
When to Use
- Comparing two independent groups
- Data is ordinal or continuous but not normally distributed
- Sample sizes are small
- Outliers are present that would skew parametric tests
Advantages
- No assumption of normal distribution
- Robust to outliers
- Can be used with ordinal data
Null Hypothesis
H₀: The two groups have the same distribution. Exact permutation inference requires exchangeability under this null. Interpreting a difference as a shift in medians additionally requires similarly shaped distributions.
