If you have two groups and you want to test for the differences in the groups after you account for age, you need to do this in two steps. First, set up a DODS model (ie, each group gets an intercept and a slope). Use this to test for a difference between the slopes of the groups ([0 0 1 -1]). If there is a difference, then you'll need to talk to a statistician to figure out what to do. If there is no difference, then set up a new DOSS model (ie, each group gets its own intercept but they share a slope), then test the difference between the groups with [1 -1 0].
doug Antonella Kis wrote: > Thanks Doug, I followed your advise and it worked. > I would like to ask you one more favour please: if using GLM I want to > compare two groups and consider age as a covariate, does this mean > that we account for age or we are regressing out the effect of age? Is > this right? In this case can I consider the contrast matrix to be [1 > 0] since we need to add zero for the variable which are covariate? > > Thank you. > AK > > ------------------------------------------------------------------------ > *From:* Douglas N Greve <gr...@nmr.mgh.harvard.edu> > *To:* Antonella Kis <ator...@yahoo.com> > *Cc:* "freesurfer@nmr.mgh.harvard.edu" <freesurfer@nmr.mgh.harvard.edu> > *Sent:* Tuesday, September 27, 2011 11:17 AM > *Subject:* Re: Clusters formation by FDR > > Why not run mri_glmfit-sim? It will give you the file that you want, > and it will be easier than me explaining all the stuff you'd need to > do to get it otherwise. > doug > > Antonella Kis wrote: > > Good morning Doug, > > > > > > I will really appreciate if you can give me an advise on how I can > get the mean average of the cortical thickness value for the FDR > clusters so before Monte Carlo Simulation. > > > > Many thanks, > > Antonella > > > > > > -- Douglas N. Greve, Ph.D. > MGH-NMR Center > gr...@nmr.mgh.harvard.edu <mailto:gr...@nmr.mgh.harvard.edu> > Phone Number: 617-724-2358 Fax: 617-726-7422 > > Bugs: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting > FileDrop: www.nmr.mgh.harvard.edu/facility/filedrop/index.html > > > > The information in this e-mail is intended only for the person to whom > it is > addressed. If you believe this e-mail was sent to you in error and the > e-mail > contains patient information, please contact the Partners Compliance > HelpLine at > http://www.partners.org/complianceline . If the e-mail was sent to you > in error > but does not contain patient information, please contact the sender > and properly > dispose of the e-mail. > > > -- Douglas N. Greve, Ph.D. MGH-NMR Center gr...@nmr.mgh.harvard.edu Phone Number: 617-724-2358 Fax: 617-726-7422 Bugs: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting FileDrop: www.nmr.mgh.harvard.edu/facility/filedrop/index.html _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
