11.7. Non-parametric equivalents of the t-test

The t-test is a test for difference of means. It is suitable for data drawn from a normal distribution, even if the sample size is small.

If the data are not drawn from a normal distribution, or we cannot be confident that they are, we can use a permutation test (see last week) or a non-parametric test based on ranks.

Just as we have different versions of the t-test, we have different rank-based non-paramteric tests for

• independent samples

• paired samples

These are reviewed in the following pages