Hi Bryan,
Thanks so much for your detailed response. This is incredibly helpful. I have some follow-up questions for you before I go on my merry way:
1. The time interval between time point 1 and time point 2 in my sample (all kids) ranges from 1.21 years to 2.43 years. Can modified swe handle this variability? Or is classic swe more appropriate?
2. If I'm understanding your instructions on how best to handle age and time interval between scans, I'll first average age at time 1 and age at time 2; for subjects with 1 time point only, average age will be age at scan. Then, I'll mean center these computed ages in my design.mat file. Would I do this separately by group as described below in my design.mat file?
3. Finally, can you confirm that the design.con I have below correctly models contrasts for the main effect of group, the main effect of time, and the interaction of group by time? Is site and sex also modeled appropriately?
Thanks again for your guidance!
Lara
[design.sub]
Subj time point group
13649 1 1
13649 2 1
15388 1 1
15341 1 1
15341 2 1
…..
15403 1 2
15350 1 2
15350 2 2
15398 1 2
15398 2 2
[design.mat]
control patient ageControl agePatient intervalControl intervalPatient sex site 1 site2 site3 site4 site5
1 0 0.678 0 -1.25 0 1 1 0 0 0 0
1 0 0.678 0 1.25 0 1 1 0 0 0 0
1 0 -1.272 0 0 0 0 2 1 0 0 0
1 0 -0.042 0 -1.3 0 0 3 0 1 0 0
1 0 -0.042 0 1.3 0 0 3 0 1 0 0
0 1 0 1.116 0 0 1 2 0 0 1 0
0 1 0 0.356 0 -1.5 0 1 0 1 0 0
0 1 0 0.356 0 1.5 0 1 0 1 0 0
0 1 0 -0.914 0 -2 0 3 0 0 0 1
0 1 0 -0.914 0 2 0 3 0 0 0 1
[design.con]
group 1 -1 0 0 0 0 0 0 0 0 0 0
time 0 0 0 0 0.5 0.5 0 0 0 0 0 0
group by time 0 0 0 0 1 -1 0 0 0 0 0 0
group by time 0 0 0 0 -1 1 0 0 0 0 0 0
########################################################################
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