Welch analysis of variance

The classical analysis of variance assumes that all groups vary equally. The Welch analysis does not: it weights each group by its spread and reduces the degrees of freedom (hence the decimals). Statable always gives it as the main result, without a pre-test; the classical analysis of variance is shown next to it.

Example: Welch F(4, 42.7) = 8.03, p < .001: the ozone values of the five months differ even when the spreads are unequal.

Caution: The Welch analysis also only shows that at least two groups differ. The pairwise comparisons show which ones (Games-Howell fits).