Usage of parametric and nonparametric statistics

To decide whether to use parametric or nonparametric statistics, you should consider several criteria about the sample data and the assumptions, and carefully evaluate the validity of those assumptions.

Consider the following criteria for the decision making:

Parametric statistics are more powerful for the same sample size than nonparametric statistics.
Parametric statistics use continuous variables, whereas nonparametric statistics often use discrete variables.
If you use parametric statistics when the data strongly diverts from the assumptions on which the parametric statistics are based, the result might lead to incorrect conclusions.
Nonparametric statistics usually can be done fast and in an easy way. They are designed for smaller numbers of data, and also easier to understand and to explain.