I don't think you are modeling gender and scanner appropriately. It looks like you have them as continuous covariates? The right way is to create classes. In your case, you'd have 8 classes, Group1MaleScanner1, Group1FemaleScanner2, etc.
On 09/15/2016 10:48 AM, Eryilmaz, H. Hamdi wrote: > Dear Doug/FreeSurfers, > > We are looking at effects of age-squared on cortical thickness in two > different groups. We are interested in age-squared by group > interactions on cortical thickness across the surface. Nuisance > covariates include age, sex, scanner, and total brain volume. > > The sig map for the interaction shows numerous highly significant > regions. When we extract cortical thickness from individual subjects > for these regions, and then plot the relationship between age-squared > and cortical thickness (after adjusting for the covariates) in group 1 > versus group 2, the interaction is very clear. > > However, using linear regression in SPSS, we are not able to reproduce > these results. I suspect we are not using the same model in SPSS that > FreeSurfer is using to do the interaction analysis. > > This is how our fsgd file looks like: > > GroupDescriptorFile 1 > Title GroupAgesqInteraction > Class Group1 > Class Group2 > Variables Agesq Age Gender Scanner TBV > > Input 3662291 Group1 0.607 0.654 -1.061 1.041 0.706 > Input 3665043 Group1 1.294 1.237 -1.061 1.041 -0.747 > . > . > > This is the contrast we used: > > [0 0 1 -1 0 0 0 0 0 0 0 0] > > What would be the translation of this contrast to a linear model, > where we are interested in the age -squared by group interaction on > cortical thickness after controlling for the four nuisance covariates? > > Thanks very much! > > Hamdi and Josh > > > > > _______________________________________________ > 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.
