A non parametric test (sometimes called a distribution free test) does not assume anything about the underlying distribution (for example, that the data comes from a normal distribution). That’s compared to parametric test, which makes assumptions about a population’s parameters (for example, the mean or standard deviation); When the word “non parametric” is used in stats, it doesn’t quite mean that you know nothing about the population. It usually means that you know the population data does not have a normal distribution.
This topic covers: Sign Test, Types of sign test, Wilcoxan’s signed rank sum test, Requirements for running the test, Wilcoxan’s signed rank test, Mann Whitney U Test, Kruskal-Wallis test.