Hypothesis tests are parametric tests when they assume the population follows some specific distribution (such as normal) with a set of parameters.
Nonparametric tests, on the other hand, are employed when certain assumptions cannot be made about the population. Rank or ordinal data usually require nonparametric analysis.
Nonparametric tests are also referred as distribution-free methods. Since they make fewer assumptions, they are more robust than their corresponding parametric ones.
OriginPro offers the following nonparametric hypothesis tests: