Gang,
Hello, I've run with this dataset and ran into an issue where calculations in R and SPSS didn't match.
I ran my 2 x 2 mixed model using 3dMVM
Here is the breakdown:
2 Factors:
group - between subject 2 levels (with, without)
scan - within subject 2 levels (pre, post)
We generated a group x scan interaction map and looked at the interaction post-hoc comparisons from that map.
I was able to replicate the findings in R from extracted cluster peak voxels.
I get the same results in AFNI and R (using lme) for the following contrasts:
Group main effect - ( t contrast group1 vs group2, collapsed across scan)
Scan main effect - (t contrast pre vs post, collapsed across group)
group1_Scan1_vs_Scan2
group2_Scan1_vs_Scan2
However, for the following two contrasts:
scan1_Group1_vs_Group2
scan2_Group1_vs_Group2
I get different t scores in AFNI than I do R and SPSS. Not sure as to why. I thought maybe it was my model setup with lme, but I was able to replicate different findings in SPSS. Your help would greatly be appreciated.
Thank you for your time.
Michael
