Thank you so much.
Very helpful.
SS
-----Original Message-----
From: FSL - FMRIB's Software Library [mailto:[log in to unmask]] On
Behalf Of Michael Harms
Sent: Wednesday, April 04, 2012 1:47 PM
To: [log in to unmask]
Subject: Re: [FSL] Demeaning parameters in un-paired two group
comparison
In general you want to use the grand mean. See previous posts on this
topic in the archives, or Jeanette Mumford's web page on mean centering.
cheers,
-MH
On Wed, 2012-04-04 at 13:29 +0100, Seyed Sajjadi wrote:
> Hi,
>
>
>
> I have a question regarding designing matrices in fsl.
>
> I am trying to design a matrix for un-paired two groups comparison
> (patients vs. controls) with one nuisance factor (grey matter volume).
> I understand that I need two separate columns for patients and
> controls to enter the GMV values for each group in a separate column.
> Now, to demean the grey matter volumes do I have to use the grand mean
> (mean of both groups put together) or group specific means (demeaning
> patients value by patients' mean and controls by controls' mean)?
>
>
>
> Best wishes
>
> Seyed Sajjadi
>
>
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