[Freesurfer] long_stats results for group analysis

Hi

I run the commands listed below and I was wondering if there is a way to get the average pc1 for each group. I get an average for the entire sample. What should I use instead of --osgm?

long_stats_slopes --qdec ./qdec/long.qdec.table.dat --stats aseg.stats --meas volume --sd $SUBJECTS_DIR --do-rate --do-pc1fit --do-pc1 --do-spc --time years --stack-rate ./qdec/long_3groups.aseg-rate.stack.txt --stack-pc1fit ./qdec/long_3groups.aseg-pc1fit.stack.txt --stack-pc1 ./qdec/long_3groups.aseg-pc1.stack.txt --stack-spc ./qdec/long_3groups.aseg-spc.stack.txt

mri_glmfit --osgm --glmdir long_3groups.aseg-pc1 --table ./qdec/long_3groups.aseg-pc1.stack.txt