Imagine comparing session durations between two groups of pages: those with a featured snippet and those without. You run a Student’s t-test and get a p-value of 0.08. Not significant, apparently. But looking at the data, you notice the distributions are heavily skewed: a few pages with very long sessions, many with very short ones. The t-test assumes normality, and here we are light-years away.
The Wilcoxon test is a non-parametric test that makes no assumptions about the shape of the distribution. It works on ranks, not on original values: it orders all data from smallest to largest and assigns scores based on position. This makes it especially useful in SEO, where many metrics (sessions, CTR, rankings) are anything but normal.
Continue reading “Non-Parametric Tests: The Wilcoxon Test for Non-Normal Data (with R Examples)”