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Nonparametric Statistics
A set of data analysis methods not based on the assumption of normality of the data. They are sometimes referred to as being “distribution free,” but that is misleading. They are not distribution free, but nor are they based on the normal distribution sampling; thus they are “normal distribution free.” These tests are often used to compare medians, proportions, or frequencies or as an alternative to parametric methods to compare centrality when assumptions are not met. Generally, they have slightly lower statistical power than their parametric counter parts.