Dear SPM mail list,
I would like to calculate 'effect sizes' from a ROI in two groups of subjects. Does this sound like a correct way to do this? : I run my 2nd level GLM and in the results I extract the fist eigenvariate values from my ROI. I get one value per subject in the work space (I am classing this as my 'effect size' for this subject for the given contrast in my ROI). But should I threshold my original map at P<0.001 or P<0.99 (so as to catch all activation)?
Sorry if this is an extremely dumb question, but would someone also be able to explain to me why I get different values for the effect size for each subject if I do the above but for eg only one treatment group at a time? again, apologies for my ignorance.
Any help is much appreciated,
Anjie
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