A Monte Carlo Study of Analysis of Covariance Under Violations of the Assumptions of Normality and Equal Regression Slopes

The present study indicates that ANCOVA is robust with respect to dual violations of the assumptions of equal regression slopes and normality of distributions provided that group sizes are equal. In ad dition, when regression slopes are equal, ANCOVA appears to be robust to violations of the assumption of normality whether group sizes are equal or not. In the present study ANCOVA did display disruptions of empirical significance levels when unequal regression slopes and unequal group sizes were coupled with nonnormal distri butions.