Hello Douglas,
If I understand your comment about defining all discrete variables as classes
(e.g. PT_F, PT_M, HC_F, HC_M) *only applies* to glm command line stream not
qdec. If I am using qdec I can have discrete variables defined separately (e.g.
Sex, Diagnosis) specified in the qdec.table text file as I am not required to
specify classes as in the FS descriptor file. I am following here the
instructions as shown below. Do I understand correct?
Thanks,
Pablo
qdec.table example from FSpage
> To: freesurfer@nmr.mgh.harvard.edu
> From: gr...@nmr.mgh.harvard.edu
> Date: Mon, 21 Sep 2015 17:39:14 -0400
> Subject: Re: [Freesurfer] Qdec: group differences covaring for age and sex
>
> Yes, it is addressing that question. The contrast should be the same as
> your Group Diff below. Although I'm not sure you're using the proper
> design. It looks like you are using Sex as a continuous covariate? That
> is not correct. It should be discrete. So you should have 4 classes
> (HC-M, HC-F, PT-M, PT-F)
>
> On 09/21/2015 09:31 AM, pablo najt wrote:
> > Hello FS experts,
> > I would like to understand the results from qdec in a GLM model with
> > Group (PT/HC), and two covariates (Age, gender).
> > I set up my contrast as follow:
> >
> > Group Diff
> > HC PT AgeHC AgePT SexHC SexPT
> > 1 -1 0 0 0 0
> >
> > Group x Age effect
> > HC PT AgeHC AgePT SexHC SexPT
> > 0 0 1 -1 0 0
> >
> > Group X Sex effect
> > HC PT AgeHC AgePT SexHC SexPT
> > 0 0 0 0 1 -1
> > Continues just as indicated in the "2 Groups 2 Covariates example"
> >
> > What I would like to find out: /If there are group differences while
> > controlling for age and sex/.
> >
> > In Qdec I selected Group, Gender, and Age. (Age as normal variable,
> > not as nuisance)
> > However, when I open my results with Qdec I am not quite sure it is
> > answering my question.
> >
> > From all the questions listed I thought that the following was
> > addressing what I need, but would like to clarify.
> > "/Does the thickness, --Age correlation, accounting for Gender, differ
> > between HC and PT?"/
> > Would you mind confirming this for me?
> > Thanks!!
> > Pablo
> >
> >
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>
> --
> Douglas N. Greve, Ph.D.
> MGH-NMR Center
> gr...@nmr.mgh.harvard.edu
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>
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