Are you sure your R design matrix and contrasts are consistent with FS? Also, something could have gone wrong in the transfer to each subject. I would recommend extracting the data directly out of the input file (y.mgh) using mri_segstats with --slabel, especially if the label is small.
On 03/28/2014 12:15 PM, Clint Johns wrote:
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