(a) The underlying population are normally distributed in terms of the dependent variable. (b) The variances of the dependent variables in each population from which the samples were taken should be (roughly) equal.
Work Step by Step
(a) This is not a strict requirement, but if normality is obviously violated, then we turn to some nonparametric tests. (b) If this assumption is violated, we again tum to the use of nonparametric tests.