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.shur...@gmail.com <mailto:ashley.shur...@gmail.com>> wrote:
>
> Thank you!
>
>
> On Tue, Oct 29, 2013 at 10:19 AM, Douglas N Greve
> <gr...@nmr.mgh.harvard.edu <mailto:gr...@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.
> MGH-NMR Center
> gr...@nmr.mgh.harvard.edu <mailto:gr...@nmr.mgh.harvard.edu>
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--
Douglas N. Greve, Ph.D.
MGH-NMR Center
gr...@nmr.mgh.harvard.edu
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