It would be the same as your 2nd matrix with the right four columns negated.
doug Stefan Brauns wrote: > Hi all, > > I am trying to examine the interaction of 2 factors (2 x 4 groups) > and have difficulties to find the right contrast matrix for mri_glmfit. > > We have patients and controls at four different aquisition sites and > want to know if the changes (i.e. thickness) between patients and > controls are equal in every site. > > so we have 8 groups: > > patientssite1 > patientssite2 > patientssite3 > patientssite4 > controlssite1 > controlssite2 > controlssite3 > controlssite4 > > the contrast for differences between patients and controls (T-Test) > would be: > > 1/4 1/4 1/4 1/4 -1/4 -1/4 -1/4 -1/4 > > the contrast to investigate if the observed measured value is equal in > all sites (F-Test) would be: > > 1/2 -1/2 0 0 1/2 -1/2 0 0 > 0 1/2 -1/2 0 0 1/2 -1/2 0 > 0 0 1/2 -1/2 0 0 1/2 -1/2 > > How would the contrast matrix look like if I want to test if there is > an overall interaction between site and diagnosis, i.e. does the > effect of diagnosis vary by site (F-Test)? > > Many thanks, > Stefan > > -- > Stefan Brauns > > ------------------------------------------------------------------------ > > _______________________________________________ > Freesurfer mailing list > Freesurfer@nmr.mgh.harvard.edu > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer -- Douglas N. Greve, Ph.D. MGH-NMR Center gr...@nmr.mgh.harvard.edu Phone Number: 617-724-2358 Fax: 617-726-7422 In order to help us help you, please follow the steps in: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
