In your case you have HC listed first, so red/yellow means HC>SAD, blue means SAD>HC
doug

On 10/29/2013 11:03 PM, Ashley Shurick wrote:

Hi Doug,

Apologies, but I have a rather easy follow-up question that I can't figure out:

How do you interpret the effect in each significant region? A previous post suggests using ctrl + left mouse click on a blob and examining the plot of the data. However, for the model I am looking at ("Does the thickness-ERQ correlation differ between HC and SAD?") I still can't determine if cortical thinning represents HC<SAD or SAD<HC. I'm attaching a representative plot here.

Thank you,

Ashley

On Tue, Oct 29, 2013 at 10:25 AM, Ashley Shurick <ashley.shurick@gmail.com <mailto:ashley.shurick@gmail.com>> wrote:

    Thank you!


    On Tue, Oct 29, 2013 at 10:19 AM, Douglas N Greve

    <greve@nmr.mgh.harvard.edu <mailto:greve@nmr.mgh.harvard.edu>> wrote:


        On 10/29/2013 01:10 PM, Ashley Shurick wrote:
        > Hi all,
        >
        > I'm running analyses in Qdec and want to verify a few things:
        >
        > 1. When comparing two groups (HC vs patients) I am including
        mean
        > cortical thickness as a covariate, using the following equation:
        >
        >
        > bh.thickness = (lh.thickness*lh.surfarea +
        rh.thickness*rh.surfarea) /
        > (lh.surfarea + rh.surfarea)
        >
        >
        > Is this the best way to calculate global mean thickness?
        Yes
        >
        >
        > 2. I want to regress out any effects of age, therefore I need to
        > demean the ages for my groups as a whole, and not perform this
        > calculation on each group separately, correct?
        Yes, in which case the test of the difference between groups
        will be
        done at an age equal to the mean of the ages.
        >
        > 3. I'm including questionnaires as a covariate of interest -
        do I need
        > to demean these values as well?
        When you do a test on a continuous covariate, that test will be
        unaffected by demeaning of the covariate. Demeaning will
        affect the
        difference between groups if you use a separate covariate for each
        group. If you have a single covariate across groups, demeaning
        will have
        no effect.

        doug
        >
        >
        > Thank you in advance for your help!
        >
        >
        > Ashley
        >
        >
        > --
        > Ashley A. Shurick
        > Ph.D. Candidate
        > Department of Psychology
        > Stanford University
        >
        >
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        Douglas N. Greve, Ph.D.
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