External Email - Use Caution Dear Freesurfer experts,
This is the first time I perform group analysis in Freesurfer. My aim is to compare the cortical thickness in four groups matched in age, sex and years of education using the Monte Carlo multiple comparisons correction. I tried to follow the Freesufer tutorials <https://surfer.nmr.mgh.harvard.edu/fswiki/FsTutorial/GroupAnalysis> to perform this group analysis and I would be really grateful whether someone can verify that all steps are correct. For example, for the cortical thickness (smooth = 15 FWHM) of the left hemisphere, the four steps that I followed were: STEP 1. Assemble the cached Data (mris_preproc) using the fsgd file mris_preproc --fsgd STUDY_4groups.fsgd \ --cache-in thickness.fwhm15.fsaverage \ --target fsaverage \ --hemi lh \ --out lh_J4G_thickness.15.mgh \ STEP 2. Perform a GLM Analysis (mri_glmfit) mri_glmfit \ --y lh_J4G_thickness.15.mgh \ --fsgd STUDY_4groups.fsgd \ --C *group.effect.mtx* \ --surf fsaverage lh \ --cortex \ --glmdir left_hemisphere_thickness_results\ STEP 3. Perform Monte Carlo simulation mri_glmfit-sim \ --glmdir left_hemisphere_thickness_results \ --sim mc-z 10000 4 mc-z.abs \ --sim-sign abs --cwpvalthresh 0.05\ --overwrite \ *QUESTIONS:* 1. Have I followed the steps to perform the analysis correctly or do you think I forgot some important flag? 2. Before test differences between two groups (eg. group1 > group 2 with the vector 1 -1 0 0) I would like to test any group effect. For that purpose, I created the group.effect.mtx contrast file (see below), is correct? 1 -1 0 0 0 1 -1 0 0 0 1 -1 Any help would be appreciated. Best regards, Steve
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