Robustness of the Two-Sample T-Test

In the literature, one finds evidence that the two-sample t-test is robust with respect to departures from normality, and departures from homogeneity of variance (at least when sample sizes are equal or nearly equal). This evidence, presented in various articles, is usually based on an approximate approach without error analysis or on a simulation approach that is of limited extent. The present paper takes a closer and more extensive look at the quality of this procedure under departures from the primary assumptions of normality and of equal variances. The results presented are a synthesis of several previous papers by the author and colleagues, with particular emphasis on the use of a broad Monte Carlo approach to the assessment of robustness.