Am not too familiar with QDEC, but I though you can do a simple analysis with one group testing where a measure (e.g. thickness, curvature) is different from zero? If so you can do the same here, but instead of thickness you can use the thickness difference or the thickness percent change ( one file for each subject, stored in the base directory, as output from the long_mris_slopes script that you used, as described in the tutorial)?

Doug, can QDEC do something as simple as testing if some map is different from zero?

Best, Martin

On Jun 28, 2013, at 10:40 AM, Douglas N Greve greve@nmr.mgh.harvard.edu wrote:

Hi Sandra, you cannot do the longitudinal statistical analysis in QDEC. You will have to use mri_glmfit. Look at the FSGD examples on the wiki. doug

On 06/28/2013 03:28 AM, Sandra Preissler wrote:

...

Dear freesurfer experts,

we want to do longitudinal analyses for two different time points in only one group (We do not have a control group or different groups within the intervention). So we did the longitudinal processing as described in the tutorial (http://ftp.nmr.mgh.harvard.edu/fswiki/FsTutorial/LongitudinalTutorial#Prepar...). Now we tried to investigate the results with Qdec. We wanted to test whether the averaged change of thickness between pre-test and post-test differs from zero. We had the experience that we could only test the averaged thickness by choosing a discrete factor in Qdec. Our Problem is that we don’t have a control group. So we couldn't choose the group variable as discrete factor. It’s an pre-post-design with only one group.

Is it possible to investigate changes in thickness between pre-test and post-test without choosing a factor? Or do we have to create a group variable as discrete factor?

Can you help us in fixing this problem?

Thanks in advance!

Sandra

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--------------------------------- Dr. Martin Reuter Assistant in Neuroscience - Massachusetts General Hospital Instructor in Neurology - Harvard Medical School MGH / HMS / MIT

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