Homoscedasticity (homogeneity of variance):Normal-theory-based tests for the equality of population means such as the t-test and analysis of variance assume that the data come from populations that have the same variance even if the test rejects the null hypothesis of equality of population means. If this assumption of homogeneity of variance is not met the statistical test results may not be valid. Heteroscedasticity refers to lack of homogeneity of variances.