Great - and this would be true for all models?
For example, in the attached graph, I'm looking at a region representing increased cortical thickness for one group compared to the other (orange blob, Q: "Does the average thickness differ between HC and SAD?" nuisance factor: mean thickness). From this plot it appears that SAD > HC, but based on your answer to the previous question I would think this region should represent HC > SAD. Can you please explain this?
Thank you!
On Wed, Oct 30, 2013 at 7:33 AM, Douglas N Greve greve@nmr.mgh.harvard.eduwrote:
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.**comashley.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<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 > > > ______________________________**_________________ > Freesurfer mailing list > Freesurfer@nmr.mgh.harvard.edu <mailto:Freesurfer@nmr.mgh.**harvard.edu<Freesurfer@nmr.mgh.harvard.edu>> https://mail.nmr.mgh.harvard.**edu/mailman/listinfo/**freesurfer https://mail.nmr.mgh.harvard.edu/mailman/listinfo/freesurfer
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