I ran a study, where a single variable was measured repeatedly for each participant, under different conditions. Analyzing this data with SPSS has been rather straightforward, by using the General Linear Model -> Repeated Measures ANOVA, and specifying each measure in the within-subject factors.
My problem arises when I try to include some post-experiment data I collected, like a test that all participants completed after the experiment, with integral scores ranging from 0-24. I want to include this to see how these scores relate to the within-subjects measures, and adding this data as a between-subject factor makes sense, but due to the nature of the test score variable I have up to 25 categories that make the data impossible to work with.
It seems like this should be a common issue, and my Googling has helped me a bit, but most of the examples I have seen use categorical variables like gender for the between-subject factors. What do I do if the between-subject factor isn't categorical?
I will be very grateful for any insight, comments and tips you have. Thanks!