what data do parametric tests require
Nonparametric Tests. Parametric tests: Require assumptions about population characteristics: normality of the underlying distribution, homogeneity of variance, known mean / variance. Examples: F, z, t tests. Nonparametric tests: Do not require assumptions about population characteristics.Can be used with very skewed distributions or when the population variance is not homogeneous. Can be used with ordinal or nominal data.ecause of violations of parametric tests, we may decide that we need to do one of the nonparametric tests. Two main procedures for ranked data: Wilcoxon test and Kruskal-Wallis test. We ll cover the Wilcoxon test only.