I apologize if I did not explain my issue properly.

I'm interested in looking at age-related thickness reductions in 1 group (patients), but I'd like to also account for the effect of disease duration.

We can say that in my case disease duration is the nuisance factor.

Briefly, I have the same issue reported in here (https://www.mail-archive.com/freesurfer@nmr.mgh.harvard.edu/msg32860.html), but with only one group.

How would you recommend to proceed?

Many thanks,

Pilar

Message: 2
Date: Wed, 27 Nov 2019 16:56:20 +0000
From: "Greve, Douglas N.,Ph.D." <DGREVE@mgh.harvard.edu>
Subject: Re: [Freesurfer] [External] Freesurfer Digest, Vol 189, Issue
36
To: "freesurfer@nmr.mgh.harvard.edu" <freesurfer@nmr.mgh.harvard.edu>
Message-ID: <fbb77a97-61b5-fac5-e2b3-0ee327e29ce3@mgh.harvard.edu>
Content-Type: text/plain; charset="utf-8"

what is the difference between and independent variable and a covariate?

On 11/27/2019 6:57 AM, Ferraro, Pilar wrote:
> External Email - Use Caution
>
> Yes, I did.
> But in this case I have two factors, not only one. In particular, I have an independent variable X and a covariate I?d like to include in the model.
> How would you suggest to proceed?
>
>
> Thanks,
>
> Pilar