Nonparametric or distribution-free statistics are a method to quantitatively assess environmental data and environmental impact. This statistical methodology is advantageous in many cases because of the computational ease and the fact that few if any assumptions are needed about the sampled populations. This is particularly important in ecological studies, since organisms are distributed typically in a clumped or patchy fashion, and the use of parametric or normal statistics is ill advised, even if data transformations are made.

Specifically ranking methods are discussed. Tests examined include the rank sum test, signed rank test, one-way analysis of variance, and two-way analysis of variance. It is shown that these statistical techniques are oftentimes the method of choice for evaluating ecological data. Examples of their use to assess ecological data and water chemistry data are given.