Hello,
Thank you for answering me. I searched mailing list and read this answer email:
I see that group.levels has four levels.  Unfortunately, right now qdec only supports two levels for a discrete factor.  One the features in the works is to increase this.
Nick Schmansky
Wed, 27 Feb 2008 11:08:10 -0800
Is this question still here? I have a five levels discrete factor. Can I run correlation statistic by Qdec?
Thanks again
Hong Xie


From: Douglas N Greve [mailto:greve@nmr.mgh.harvard.edu]
Sent: Thu 1/8/2009 4:40 PM
To: Xie, Hong
Cc: freesurfer@nmr.mgh.harvard.edu
Subject: Re: [Freesurfer] Qdec correlation analyses


It has to be interpreted as a continuous variable. The test is done
using a t-test inside the glm. This reduces to a Pearson if there  is
only one variable and no intercept (which it is not).

doug

Xie, Hong wrote:
>
> Hello, freesurfer group,
>

>
>  I have run qdec for comparing thickness between two groups. When qdec
> does a correlation analyses for thickness versus a second variable: 1)
> Does the second variable have to be a continuous interval variable or
> 2) can the second variable be an ordinal variable with more than 2
> levels? In the case of the correlation between two continuous
> variable, is the test a Pearson correlation? If 2) is possible, is the
> correlation a Spearman correlation?
>
> Thank for your help,
>

>
> Hong Xie
>
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