Hello Doug, Thank you for your reply. I misused the word contrast, when I should have said design matrix. It looks at though I should be able to look at an interaction effect between two variables but ignore another. In the case of the example https://surfer.nmr.mgh.harvard.edu/fswiki/Fsgdf2G2V you could be able to look at the interaction between Group and Age while ignoring (or controlling) for the effects of weight. But maybe this is not possible to do with a categorical variable?
I have also considered using a four group design as shown in https://surfer.nmr.mgh.harvard.edu/fswiki/Fsgdf4G1V, where you concatenate two categorical variables however, I dont think you can look at interaction effects between those variables anymore. So I'm still wondering if it is possible to look at the interaction between two categorical variables using fsgd? GroupDescriptorFile 1 #Title SZ vs HC Class HC Class SZ Variables Score Sex Age Input 130 HC high m 50 Input 277 HC low f 53 Input 190 HC low m 25 Input 201 SZ high f 29 Input 250 SZ high f 52 ... Group difference.mtx 1 -1 0 0 0 0 0 0 Group by Score interaction .mtx 0 0 1 -1 0 0 0 0 But this doesn't and should work. How should I proceed? Thanks again, Lindsay -- Lindsay Hanford, BSc, PhD Candidate McMaster Integrative Neuroscience Discovery & Study | *Department of Psychology, Neuroscience & Behaviour * McMaster University *|* 1280 Main Street West, PC329 Psychology Building *|* Hamilton, ON, L8S 4L8 905 525 9140 x24784 *|* lindsay.hanf...@gmail.com
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