# Non-parametric statistics

**Non-parametric** (or distribution-free)

**inferential statistical methods** are mathematical procedures for

statistical hypothesis testing which, unlike

parametric statistics, make no assumptions about the

frequency distributions of the variables being assessed. The most widely used of these methods is probably the

chi-square test. Other widely used non-parametric methods include

Mann-Whitney U, the Kruskal-Wallis one-way analysis of variance, the

median test,

Spearman's &rho, and estimation of probability using the

binomial distribution.

They *may* have more statistical power than a parametric test when the assumptions underlying the parametric test are not satisfied.

See also parametric statistics.