Hi,
I have a follow-up question about demeaning, specifically applied to running linear mixed effects models.
For example, we have a design matrix X with the following columns: intercept (all ones) age gender age*age pubertal status
If we want to look at the effect of age*age, controlling for pubertal status and gender [0 0 0 1 0 ], should age be demeaned prior to calculating the interaction term? I presume so, because if not, age*age will be highly correlated with age. I also presume that the covariate pubertal status should be demeaned?
Thanks,
Sarah ________________________________________ From: freesurfer-bounces@nmr.mgh.harvard.edu [freesurfer-bounces@nmr.mgh.harvard.edu] on behalf of Douglas N Greve [greve@nmr.mgh.harvard.edu] Sent: Tuesday, 5 August 2014 2:09 AM To: amirhossein manzouri; free surfer Subject: Re: [Freesurfer] effect of demeaning the age
check out this web page http://mumford.fmripower.org/mean_centering/
On 08/04/2014 12:01 PM, amirhossein manzouri wrote:
Hi, I am looking at group differences between patients(20) and controls(n=20). I get significant results when I use Age, while I get no significance using Demeaned age both with DODS, also the pattern of significance is different. Would you please explain why?
Best regards, Amirhossein Manzouri
-- Douglas N. Greve, Ph.D. MGH-NMR Center greve@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.