That would be especially helpful, thanks Doug. I have another related question. In addition to measuring cortical thickness, I've also done the same analysis using the cortical surface volume measure in Qdec. For this analysis I used age and mean centered total intercranial volume (TIV) as nuisance variables. After running the analysis, the graph is displayed showing the volume on the y axis and mean centered TIV on the y axis. When I extract the data I get volume values in the 2.0016 - 2.7268 range, I was expecting to see values on the order of 1500-1600 or so, is this because qdec is giving me cortical volume values that have been normalized to TIV?

Thanks again for all your help!


On Wed, Jun 25, 2014 at 5:03 PM, Douglas N Greve <greve@nmr.mgh.harvard.edu> wrote:

No, I've never used SPSS. If you know matlab, I can step you through how
to do it there

On 06/25/2014 04:13 PM, Emma Thompson wrote:
> I'm using SPSS. I'm not sure if my analysis reflects exactly what qdec
> is doing, do you know which analysis in SPSS would be most
> appropriate? I'm doing a simple ANCOVA.
>
>
> On Wed, Jun 25, 2014 at 11:07 AM, Douglas N Greve
> <greve@nmr.mgh.harvard.edu <mailto:greve@nmr.mgh.harvard.edu>> wrote:
>
>
>     what software did you use? Are you sure you are using the same
>     model as
>     qdec uses?
>
>
>     On 06/25/2014 11:03 AM, Emma Thompson wrote:
>     > Thanks Doug, yes I did control for age in both instances.
>     >
>     >
>     > On Wed, Jun 25, 2014 at 10:14 AM, Douglas N Greve
>     > <greve@nmr.mgh.harvard.edu <mailto:greve@nmr.mgh.harvard.edu>
>     <mailto:greve@nmr.mgh.harvard.edu
>     <mailto:greve@nmr.mgh.harvard.edu>>> wrote:
>     >
>     >
>     >     Your interpretation is right (ie, controls > patients for
>     >     red/yellow/orange). When you compared the two groups in your
>     separate
>     >     analysis, did you control for age?
>     >     doug
>     >
>     >
>     >     On 06/24/2014 02:19 PM, Emma Thompson wrote:
>     >     > Hi Freesurfers,
>     >     > I am reposting this as my last email bounced.
>     >     >
>     >     > I have conducted a DODS analysis in qdec with group
>     (controls vs
>     >     > patients) set as my fixed factor and age as a nuisance
>     variable to
>     >     > determine if my groups differ in cortical thickness.
>     Controls were
>     >     > added first in the .levels file followed by patients. When I
>     >     view the
>     >     > results in the display window for "do controls differ from
>     >     patients in
>     >     > cortical thickness" I see a significant cluster for the caudal
>     >     > anterior cingulate, denoted by a red-orange blob and a
>     positive
>     >     > t-value. I'm wondering if this simply means that controls had
>     >     greater
>     >     > cortical thickness compared to patients after controlling for
>     >     age? The
>     >     > reason I ask is that I'm a little confused since when I
>     created
>     >     an ROI
>     >     > for this cluster using tksurfer and then extracted the
>     means and
>     >     sd, I
>     >     > see that the patients actually have larger means than the
>     controls,
>     >     > the opposite of my interpretation of the results presented by
>     >     the qdec
>     >     > display. Furthermore, if I extract the means and sds for
>     the entire
>     >     > caudal anterior cingulate using the aparc file, I get
>     means that are
>     >     > larger in controls, compared to patients, which seems
>     consistent
>     >     with
>     >     > qdec. Any ideas? Thanks for all the help.
>     >     >
>     >     >
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>     >     --
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>     >     MGH-NMR Center
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>     <mailto:greve@nmr.mgh.harvard.edu <mailto:greve@nmr.mgh.harvard.edu>>
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>     --
>     Douglas N. Greve, Ph.D.
>     MGH-NMR Center
>     greve@nmr.mgh.harvard.edu <mailto:greve@nmr.mgh.harvard.edu>
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--
Douglas N. Greve, Ph.D.
MGH-NMR Center
greve@nmr.mgh.harvard.edu
Phone Number: 617-724-2358
Fax: 617-726-7422

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