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
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