I looked at whether participants recycled after being subjected to a given message. There were three groups: a Control group, group A, and group B.
Since my dependent measure was dichotomous (recycling vs. using the waste bin), I performed a logistic regression in SPSS. However, SPSS only let me compare individual groups to the Control group. I found that group A recycled more than controls, but group B did not.
What I am curious about now is whether group A recycled significantly more than group B.
Is it possible to do such a post-hoc test? If so, how?