ABSTRACT
ANOVA (analysis of variance) is introduced for the analysis of more than two conditions. It is a powerful parametric procedure for testing the differences between means of several levels, not just two, of one independent variable and between the means of levels of several independent variables. All the multi-level and multi-factorial tests we will cover are designed to take into account the fact that we are comparing several groups at once. They give us the probability that groups would differ as they do given that the null hypothesis is true. To reiterate a point: if there is a significant effect for our caffeine independent variable, we would expect the variation within the samples (known as the within groups variance) to be small compared with the variation of the sample means (known as between groups variance).
