Next section: Tukey's HSD

In the example, if a seventh treatment condition were included and the population mean for the seventh condition were very different from the other six population means, an analysis of variance would be likely to reject the omnibus null hypothesis. So far, so good, since the omnibus null hypothesis is false. However, the probability of a Type I error in one or more of the 15 t-tests computed among the six treatments with equal population means is about 0.10. Therefore, the LSD method provides only minimal protection against a high EER.

Homogeneity of variance is typically assumed for Fisher's LSD procedure. Therefore, MSE, the estimate of variance, is based on all the data, not just on the data for the two groups being compared. In order to make the relationship between Fisher's LSD and other methods of computing pairwise comparisons clear, the formula for the studentized t (t

Next section: Tukey's HSD