Parameters are characteristics of the population being studied such as a mean (μ), standard deviation (σ) or median (Md). Statistics describe characteristics of a sample. Sample mean (&NA;) and sample median (m) are two examples. In traditional or classical parametric statistics, making inferences from a sample or samples to a population or populations necessitates assumptions about the nature of the population distribution such as a normal population distribution.

Nonparametric statistics may be defined as statistical methods that contribute valid testing and estimation procedures under less stringent assumptions than the classical parametric statistics. However, there is no general agreement in the literature regarding the exact specification of the term "nonparametric statistics." In the past, nonparametric statistics and the term "distribution-free methods" were commonly used interchangeably in the literature, although they have different implications. Nonparametric statistics were often referred to as distribution-free statistics because they are not based on a...