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Dear FreeSurfer experts,
I have two groups and two time points and I would like to do a correlation analysis between a variable (cognition) and the change score in cortical thickness between the two time points (time2 minus time1).
I would like to see if the *correlation *is *different *among each group, if there is an interaction with the group.
I have followed the paired t test instructions ( https://secure-web.cisco.com/11YHUupGYyGBe5w6QAQb3OOLcNluK0Tqv4VUmAmDx5wuogv...), but I am not sure about the contrast(s) I have to use.
The paired-diff.fsgd file (second fsgd file) is the following:
GroupDescriptorFile 1 Title OSGM Class Group1 Class Group2 Variables cognition Input subject1pair Group1 0.546 Input subject1pair Group2 -0.243 ...
How should it be the contrasts files to see the *correlation *of the variable cognition with the change score in thickness taking into account the groups? And should I use DODS or DOSS?
Using DODS: 0 0 0.5 0.5 or 0 0 1 -1
I don't understand the difference between both contrasts. I think I should use the one of "0 0 1 -1" to see whether the cognition variable correlates with change in thickness differently according to the group. Is this correct?
Using DOSS: 0 0 1
Thank you very much in advance.
Kind regards,
Agurne