In general (not specific to neuroimaging) it is not necessary to transform both the response and predictor variables.
e.g. Using log(Y) is just as acceptable as using Y; although your interpretation will have to change.
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From: FSL - FMRIB's Software Library [[log in to unmask]] on behalf of Andreas Werner [[log in to unmask]]
Sent: Thursday, March 27, 2014 10:51 AM
To: [log in to unmask]
Subject: [FSL] Aw: Re: [FSL] fix - regress out motion confound
Thank you for your quick reply.
--It's not important to......to the extent that I don't really understand where the question is coming from ;-)
I am studying this script to learn how regressing out confounds is professionally done and implemented as this is a processing step often needed.
In the mentioned script, z-transformed motion confounds are agressively regressed out of a) the z-transformed melodic_mix matrix and b) the untransformed filtered_func_data file.
I was curious to know, why z-transformation was not applied to filtered_func_data, as I presumed that in a GLM(Y=X*b) both X(=confounds) and Y(=melodic_mix or filtered_func_data) must be transformed to stay consistent.
As I understand this is is not important in the context of regressing out.
Thank you for pointing that out!
Cheers.
Gesendet: Donnerstag, 27. März 2014 um 14:39 Uhr
Von: "Stephen Smith" <[log in to unmask]>
An: [log in to unmask]
Betreff: Re: [FSL] fix - regress out motion confound
Hi
On 27 Mar 2014, at 13:22, Andreas Werner <[log in to unmask]> wrote:
Dear Experts,
studying the FIX scripts (fix_3_clean.m) I noted that motion parameter confounds are z-transformed (mean removed and normalized to unit variance aross time) before they are regressed out.
maybe - but that will have no effect on their regression out of the data timeseries - that linear transformation doesn't affect the "space they span", in GLM lingo.
Melodoc_mix is also z-transformed, but the
filtered_func_data is not. Why ?
It's not important to......to the extent that I don't really understand where the question is coming from ;-)
Cheers.
Do you generally recommend to z-transform motion parameters before regression rather than just use the untransformed entries in prefiltered_func_data_mcf.par ?
Cheers,
Andreas
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