I'm hoping to run a longitudinal analysis looking at 2 groups (controls and patients) at two time points (baseline and follow-up) for an fMRI working task in a developmental sample. Some individuals only have follow-up data at 52 weeks and others only have at 104 weeks. I am hoping to optimize sample size by using whichever follow-up time point is available. I assume I need to include a covariate for time to account for this. I'd also like to add in a few other covariates such as sex and neuropsych score.
My current plan is to:
1) Create difference contrasts for each group (ie: group baseline > group follow-up).
2) Run 1 sample t-test on the difference maps with time, sex, and neuropsych as covariates.
I'm only interested in looking at the groupXtime interaction while adjusting for sex and neuropsych score. Is this analysis plan appropriate? I reviewed the listserv on 2x2 rm anovas and the suggested model in which I put both groups in the model and look only at the interaction and main effect of time doesn't seem viable given the time point issue. If my plan is incorrect, are there other options I can use?
Thanks in advance for the help!
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