Analysis of variance: variably complex.

• Although relatively robust to the following, ANOVA assumes • Normal distribution of residuals • Variation in each group is similar • ANOVA is sensitive to outliers, and transforms of the data may be necessary • ANOVA is a test of group differences: do at least two of the means differ from each other? • Two-way ANOVA tests a number of sources of variability • It is important to know which source of variation is of interest • Do the sources of variation interact? • Care is needed with repeated measures • There may be better tests, particularly if the factor can be expressed as a continuous variable.