Post hoc results are valid to the extent that the standard F statistic is robust to violations of assumptions. As mentioned before, the F statistic is robust to unequal variances when sample sizes are equal or nearly equal. However, when both the variances and the sample sizes differ, the standard F statistic lacks power and is prone to give incorrect results. This section discusses two analysis of variance methods available in the One-Way ANOVA procedure that provide an alternative in these circumstances.

The management of a local bank has received complaints about the amount of time that customers spend waiting in line at one of their facilities. In response, analysts have recorded wait times at that facility and two other area banks for comparison purposes.

This example uses the file waittime.sav.