Sorry about previous post (Re : [FSL] longitudinal study), but I realized I did not attach the document. Here is what I talk about. I want to know if this is still the best way to analyze longitudinal FA_Change between two different groups. Now, when talking abnout the difference between twot ime points, do you refer to the skeleton images or what images in the tbss pipeline process?
Thanks in advance.
Rodrigo
Hey Naroa,
> We are trying to perform a longitudinal study with VBM and
> TBSS. We already processed all the images, but now we're not
> sure on how designing the matrix and the contrast to run the
> randomise. We have 2 groups (patients and controls) and 2
> times (base-line and follow-up). We're are interested in
> looking at changes in each of the groups over thime and to
> the interaction between time and group. How should the
> matrix and the contrast look like?
We had a discussion with Tom recently and I think the easiest way to do this in randomise at the moment would be to take *for each subject* the difference between the two timepoints (subject 1: timepoint1 - timepoint2; subject 2: timepoint 1 - timepoint 2; etc.) and then do something like (if you have, say, 2 controls and 3 patients):
Matrix:
1 0
1 0
0 1
0 1
0 1
Contrast:
1 0 (decrease over time for the controls)
-1 0 (increase over time for the controls)
0 1 (decrease over time for the patients)
0 -1 (increase over time for the patients)
1 -1 interaction between timepoint and group
-1 1 the other direction for the interaction
Hope this helps,
Gwenaelle
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Gwenaƫlle Douaud, PhD
FMRIB Centre, University of Oxford
John Radcliffe Hospital, Headington OX3 9DU Oxford UK
Tel: +44 (0) 1865 222 523 Fax: +44 (0) 1865 222 717
www.fmrib.ox.ac.uk/~douaud
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