ABSTRACT
Whenever more than one factor is investigated in an experiment, there is a wide variety of possible outcomes. For a two-factor design, one, both or neither of the main effects and/or the interaction between the two factors may be significant. Figure 9.1 shows the structure of a typical 2×2 fully between-subjects factorial design. There are two factors, each with two levels, giving a total of four cells. Each subject only contributes one single score to the data, hence appearing in only one cell. The example has a total of 36 subjects, 9 per cell. One possible question that can be asked when the data are analysed is: is either of the main effects significant? The meaning of this question is also shown in Figure 9.1.
