Question

If your main reason for choosing a 2 x 2 design is that the interaction is of particular interest, then the best analysis would be to examine a. the main effect of A and the main effect of B. b. the main effect of A, the main effect of B, and the interaction of A and B. c. the interaction of A and B and two simple main effects. d. the interaction. e. two simple main effects.

Answer 1

d) the interaction

For a 2x2 design, there is only 1 interaction. The interaction between IV1 and IV2. This occurs when the effect of say IV2 (whether there is a difference between the levels of IV2) changes across the levels of IV1. We could write this in reverse, and ask if the effect of IV1 (whether there is a difference between the levels of IV1) changes across the levels of IV2. However, just because we can write these two ways, does not mean there are two interactions. We’ll see in a bit, that no matter how do the calculation to see if the difference scores–a measure of effect for one IV– change across the levels of the other IV, we always get the same answer. That is why there is only one interaction for a 2x2.