No, it is not necessary. doug On 05/11/2015 02:53 PM, Paul Dhami wrote: > Greetings Freesurfer experts, > > I've looked over the FS mailing list, as well as other resources (such > as Mumford's page on demeaning and fMRI data), but I was still a bit > confused, so apologizes in advance. > > I have a datatset that consists of only 1 group (an expert trained > group), and I'd like to investigate how the years of training > correlates to cortical thickness. I thus have two covariates I'd like > to include: the years of training (ranging from 6 to 18 years), and > their age (ranging from 18 to 22 years old), where I want to regress > out age (treat it as a nuisance variable). From my understanding, I > am interested in the slope rather than the intercept of this one group. > > I assume that demeaning would at least bring the intercept to the mean > of this group and not at 0 (which isn't applicable to this group), but > wasn't sure if demeaning is still necessary to investigate the > correlation between cortical thickness and years of training, while > holding age as a nuisance variable (as according to Mumford: "mean > centering a covariate will never change the inference for that > covariate"). Any input would be great. Thank you. > > Paul > > > _______________________________________________ > Freesurfer mailing list > Freesurfer@nmr.mgh.harvard.edu > https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
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