Having thought more about these analyses and consulting the link below, I have come to the following conclusion.
http://www.fmrib.ox.ac.uk/fsl/feat5/detail.html#TripledTwoGroupDifference
Conducting the triple two group difference will tell me whether or not there are clusters of activity which are significantly different between the three sessions (smoking abstinence; 0.1mg and 1.2mg nicotine). It will not tell me the direction of the difference. On observing any difference (e.g., smoking abstinence versus 0.1mg nicotine) I can then follow up with a planned comparison (e.g., paired t-test on smoking abstinence versus 0.1mg nicotine), which will tell me where there are clusters of significantly more activity in the smoking abstinence session and likewise for the 0.1mg session.
Would this be correct?
Liam.
*******************************************
Liam Nestor, Ph.D
Office C8-523
Laboratory for Molecular Neuroimaging
Semel Institute for Neuroscience and Human Behavior
760 Westwood Plaza
Los Angeles 90024
Tel: 310-206-0655
E-mail: [log in to unmask]
*******************************************
________________________________________
From: FSL - FMRIB's Software Library [[log in to unmask]] On Behalf Of Liam Nestor [[log in to unmask]]
Sent: Tuesday, May 12, 2009 8:10 PM
To: [log in to unmask]
Subject: [FSL] Three Session Contrast
Hello there fellow FSL users
I have 20 subjects. Each subject underwent fMRI on three separate occasions
(smoking abstinence; 0.1mg nicotine; 1.2mg nicotine).
I wish to test the differences between these three sessions. This, I
understand, is really a repeated measures design.
The six contrasts I want to look at are:
smoking abstinence>0.1mg nicotine
smoking abstinence>1.2mg nicotine
0.1mg nicotine>smoking abstinence
0.1mg nicotine>1.2mg nicotine
1.2mg nicotine>smoking abstinence
1.2mg nicotine>0.1mg nicotine
What would be best way to perform these ananyses in FSL? I know a simple
paired ttest in FSL will let me perform these six contrasts in three
separate analyses. Would this be potentially erroneous and is there a better
way of looking at the above contrasts?
Thanks in advance.
Liam.
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