ABSTRACT
Three-factor designs are frequently required in professional research and increasingly in student projects that computers are readily available to analyse the results. The design compares the three drug treatments and compares presence with absence for two non-drug treatments. For designs with three or more factors, organizing and presenting the means demands careful attention. The main effect is a comparison among the mean scores at the various levels of a factor. Simple effects are conceptually the same as the main effect, except that the comparison is among the mean scores of the levels of a factor at a single level of one of the other factors, for a first-order simple effect, or at single levels of both the other factors for a second-order simple effect. However, the meaning of three-way interaction is that the interaction between any two of the factors is different at the different levels of the third factor.
