This is a straightforward extension to the FSGD examples. You have 3 discrete factors (2 diagnosis, 2 gender, 6 centers), this yields 2*2*6=24 classes. With one covariate, you would have 24 covariate regressors (one for each class) for a total of 48. You would then need to create a contrast matrix that tests for an interaction between diagnosis and age which is also a straight-forward extension to the examples.
Having said that, I think that 48 regressors is a lot unless you have about 500 subjects. It is also possible to have a less agressive model and just have two regressors, one for each diagnosis. But you'd have to create the design matrix yourself as this is outside of the FSGD specification. On 10/05/2016 09:22 AM, charles laidi wrote: > Dear FreeSurfers, > > I would like to study the interaction between age and cortical > thickness in patients and controls. > My hypothesis is that there is an interaction and that cortical > thickness is decreasing faster with age in patients than in controls. > I have both Male and Female included in 6 different centers. > I would like to consider also Gender and Site (6 centers) as confounds. > > My understanding is that I should perform a surface based group > analysis with freesurfer. > > I am not able to find an example for my problem in the documentation > https://surfer.nmr.mgh.harvard.edu/fswiki/Fsgdf2G0V > > Would anyone had some tips to build the Fsgd file and the contrast file ? > > Thank you very much in advance. > > Best, > > Charles > > > > _______________________________________________ > 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 Bugs: surfer.nmr.mgh.harvard.edu/fswiki/BugReporting FileDrop: https://gate.nmr.mgh.harvard.edu/filedrop2 www.nmr.mgh.harvard.edu/facility/filedrop/index.html Outgoing: ftp://surfer.nmr.mgh.harvard.edu/transfer/outgoing/flat/greve/ _______________________________________________ Freesurfer mailing list Freesurfer@nmr.mgh.harvard.edu https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer 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.
