Nonparametric statistical methods are used
a. Whenever the response variable is known to have a normal distribution.
b. Whenever the assumptions for a parametric method are not perfectly satisfied.
c. When the data are ranks for the subjects rather than quantitative measurements or when it’s inappropriate to assume normality and the ordinary statistical method is not robust when the normal assumption is violated.
d. Whenever we want to compare two methods for getting a good tan.