Z-test, Student’s T-test, Paired T-test, ANOVA, MANOVA? Actually they all belong to the Parametric statistics family which assumes that sample data come from a population that can be adequately modeled by a probability distribution that has a fixed set of parameters (mean, standard deviation) aka Normal Distribution.

Parametric tests usually assume three things:

• Independence of cases: samples are independent observations
• Normality: sample data come from a normal distribution (or at least is symmetric)
• Homogeneity of variances: sample data come from a population with the same variance

However, in real life, these assumptions can hardly be met. Non-Parametric Tests have much more relaxed assumptions and they are either distribution-free or having a specified distribution but with the distribution’s parameters unspecified.

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