Hi there,
After conducting a DODS analysis (One group, four factors, one covariate), we were able to identify a region (LH pars opercularis) whose mean thickness differed when two of the four factors interacted. In order to further investigate the interaction, we obtained each participant's mean thickness by drawing an ROI (using QDEC, which also applied the mri_label2label function to map the new ROI to all the participants).
However, when we extract the thickness data in this way, and then run a glm on the ROI data (with the same four factors), the interaction is no longer significant, and instead we observe a main effects of only one of the factors.
Does anyone have an idea why there is such a disconnect between the freesurfer output and the subsequent analysis (using glm in R)?
THANKS!!
clint