Definition of Nonparametric method:
Nonparametric method refers to a type of statistic that does not require that the population being analyzed meet certain assumptions, or parameters. Well-known statistical methods such as ANOVA, Pearson's correlation, t test, and others provide valid information about the data being analyzed only if the underlying population meets certain assumptions. One of the most common assumptions is that the population data have a "normal distribution.".
Parametric statistics may also be applied to populations with other known distribution types, however. Nonparametric statistics do not require that the population data meet the assumptions required for parametric statistics. Nonparametric statistics, therefore, fall into a category of statistics sometimes referred to as distribution-free. Often nonparametric methods will be used when the population data has an unknown distribution, or when the sample size is small.
A commonly used method in statistics where small sample sizes are used to analyze nominal data. Non-parametric method is used when the researcher does not know anything about the parameters of the sample chosen from the population. Hence, this method is sometimes referred to as parameter-free or distribution-free method. The three commonly used non-parametric correlations are Spearman R, Kendall Tau and Gamma coefficients.
Meaning of Nonparametric method & Nonparametric method Definition