5. Mistakes to avoid

5.1 Don't forget that residual error is important

In ANOVA, the observation of residual dispersion is important. In concrete terms, it's this that determines whether the effects we're looking for are significant or not. Mathematically, all the mean squares (MS) are divided by the residual MS. A small residual error (= small residual MC) will have the effect of increasing the observed Fisher of the factors and their interactions. As a result, they are more likely to be declared significant.