Dear SPM:
Help. Please.
My question concerns the proper random effects statistics for performing
conjunctions.
In the Random Effects toolkit instructions Andrew suggest using
Multi-subject different conditions analysis for examining main effects, and
Multi-study different conditions analysis for examining interactions
between different studies. In my own use of the Random effects kit I find
that including more than 2 conditions in a Multi-subject analysis, even if
those conditions are contrasted in pairs, doesn't seem to estimate the
activations correctly.
If one was doing a conjunction analysis then I imagine one would use the
Multi-study analysis to combine the 2 study types. Thus one is then faced
with the curious condition whereby the activations seen in a conjunction
(multi-study analysis) may not appear to reflect the individual main
effects (multi-subject analysis). Is there a way out of this conundrum? Can
one use the main effects within each study type as shown by the multi-study
analysis??
Thanks,
Darren
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Darren R. Gitelman, M.D. E-mail: [log in to unmask]
Cognitive Neurology and Voice: (312) 908-9023
the Alzheimer's Disease Center Fax: (312) 908-8789
WWW: http://www.brain.nwu.edu
Northwestern Univ., 320 E. Superior St., Searle 11-470, Chicago, IL 60611
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