COMMENT ON A WILCOX TEST STATISTIC FOR COMPARING MEANS WHEN VARIANCESARE UNEQUAL

Wilcox (1989) has proposed an alternative to the James (1951) second-o rder statistic for comparing population means when variances are heter ogeneous. The primary advantage of his approach is its computational s implicity in determining the number of degrees of freedom for the test statistic. We show, however, that the proposed solution can be invali d. With small (but reasonable) sample sizes, population means are unde restimated, and mean differences among populations can be overestimate d as a result of unequal sample sizes. The degree to which the procedu re is invalid depends on the magnitude of the differences in sample si zes, the expected value of the observations, and the population varian ces.