Hi,

I am trying to run a cortical thickness analysis comparing four groups – my goal is to conduct an omnibus F-test testing for any group differences. I have 0 covariates/nuisance regressors.

This would be equivalent to the “Contrast 4 group.effect.mtx” in this page, for 3 groups: https://surfer.nmr.mgh.harvard.edu/fswiki/Fsgdf3G0V

But, instead of 3 groups I have 4 groups.

I thought the contrast matrix for 4 groups F-test would be:

1 -1 0 0

0 1 -1 0

0 0 1 -1

But for 3 groups it is:

1 -1 0

1 0 -1

Would you please clarify the correct contrast matrix for this test in Freesurfer mri_glmfit?

Thank you!

Andrea

-- 

Andrea Gold, Ph.D.
Section on Development and Affective Neuroscience

National Institute of Mental Health
9000 Rockville Pike MSC 2670
Bldg. 15K
Bethesda, MD 20892
Phone: 301-402-6955
Fax: 301-402-2010

Email: andrea.gold@nih.gov