Hi Donald,
Not sure if I follow your suggestion either. If gender is a degenerate
regressor in a repeated measures design, then isn't the interaction of
gender with any other factors degenerate as well?
cheers,
-MH
On Thu, 2011-05-12 at 19:56 +0200, Alexander Olsen wrote:
> Thanks for your suggestion Donald. How would you go about to set up the
> design martrix (in FEAT) in this case?
>
>
> MCLAREN, Donald wrote:
> > I'd agree on the age part since its likely everyone is a different
> > age; however, I'd add gender as a covariate and make it interact with
> > the repeated measure (essentially coding it as the covariate and also
> > as the covariate*each measure). This would allow you to investigate
> > any gender*measure interactions.
> >
> > Best Regards, Donald McLaren
> > =================
> > D.G. McLaren, Ph.D.
> > Postdoctoral Research Fellow, GRECC, Bedford VA
> > Research Fellow, Department of Neurology, Massachusetts General
> > Hospital and Harvard Medical School
> > Office: (773) 406-2464
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> > On Thu, May 12, 2011 at 1:44 PM, Alexander Olsen
> > <[log in to unmask] <mailto:[log in to unmask]>> wrote:
> >
> > Hi Michael,
> > Thank you so much for helping me. So that means that I should set
> > up the design matrices without any covariates for age and gender?
> >
> > cheers,
> > Alexander
> >
> >
> >
> > Michael Harms wrote:
> >
> > Hi Alexander,
> > Given that you are modeling the mean of each subject using a
> > repeated
> > measures design, that mean already incorporates that subject's
> > age and
> > gender as part of its estimate. That is, if you added EVs for age
> > and/or gender, those EVs can be represented as a linear
> > combination of
> > the columns modeling each subject's overall mean, and thus you
> > would get
> > a degenerate design matrix. (This wouldn't strictly be true
> > for age IF
> > the value you used for age differed across the repeated scans of a
> > subject, but unless your scans were spaced far apart
> > temporally, you
> > still might get a poorly conditioned design matrix).
> >
> > cheers,
> > -MH
> >
> > On Thu, 2011-05-12 at 01:12 +0100, Alexander Olsen wrote:
> >
> >
> > Dear FLS experts, I'm struggling a bit with setting up my
> > analysis. What I would like to do is a repeated measures
> > design with four timepoints, as in this example:
> > http://www.fmrib.ox.ac.uk/fsl/feat5/detail.html#ANOVA1factor4levelsRepeatedMeasures
> >
> > However, I would also like to add age and gender as
> > covariates in order to "remove" these effects. I hope
> > anyone can help me, or direct me to an example which
> > describes this.
> > Thank you so much in advance.
> > Alexander
> >
> >
> >
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