Hi Tim,

yes, in the 2-stage approach, you first compute the slope per subject (e.g. mm/year thinning or q mm per year volume loss) and then do a regular GLM for each subject. For that the co-variates need to be fixed per subject. The long_qdec_table command below averages the covers for you. You could also decide to always take baseline or something.

Best, Martin

On Oct 26, 2016, at 4:17 PM, Timothy Hendrickson hendr522@umn.edu wrote:

FreeSurfer Experts,

Hello I am attempting to perform a two stage longitudinal analysis. My entire data set has two time points for each participant. I understand that the subject order in the FSGD file should correspond with the QDEC file run through long_mris_slopes. In my case the FSGD file has half as many inputs as the QDEC file.

My question is would I take the covariates from TP1 and TP2 and take the average to input into the FSGD file?

If that is the case is there anything wrong with performing the long_qdec_table --qdec "qdec.table.dat --cross --out "cross.qdec.table.dat" command and using that co-variate data to input into the FSGD file?

Respectfully,

-Tim

Timothy Hendrickson Department of Psychiatry University of Minnesota Mobile: 507-259-3434 (texts okay) _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer