How can I carry out a simple main effects test using either SAS or SPSS?
You can use either SAS or SPSS to conduct these tests. For example, let’s say that you had a fairly straightforward completely between-subjects design, with a dependent variable called Y and two categorical predictors, A and B, each with two levels. Suppose that you wanted to test the effect of A for each level of B. In SAS release 6.11 or higher, you can use the SLICE option in PROC GLM, like this: PROC GLM ; CLASS a b ; MODEL y = a b a*b ; LSMEANS a*b / SLICE=b; If you are using SPSS, you can use the MANOVA command to test the same hypotheses as the SAS program shown above: MANOVA y BY a(1,2) b(1,2) /design = B A within b(1) A within b(2). More complex designs are testable with the recent SPSS GLM and SAS MIXED procedures, including within-subjects simple main effects tests.
