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 ρ, and estimation of probability using the
binomial distribution.
See also parametric statistics.