Dear FS experts
I compared two groups wrt cortical thickness using total grey matter volume as a covariate. The results obtained without the covariate (first row in the attached figure) and with the covariate modeled across both groups (doss option, second row in the figure) differed only in quantity (clusters are smaller with the covariate). However, when using the covariate with dods, the results changed completely (third row in figure) compared to doss and compared without the covariate. Then I tested (using dods) the covariates itself (using 0 0 1 -1) and get almost identical clusters (although in the opposite direction, forth row in the figure) as found in the group comparison with the covariate (dods, third row).
In my opinion, this is puzzling! Any idea?
Thanks in advance Regards Jürgen
---------------------------------------------------------------------------- Jürgen Hänggi, Ph.D. Division Neuropsychology Institute of Psychology University of Zurich Binzmuehlestrasse 14, PO Box 25 8050 Zurich, Switzerland 0041 44 635 73 97 (phone office) 0041 76 445 86 84 (phone mobile) 0041 44 635 74 09 (fax office) BIN 4.D.04 (office room number) j.haenggi[at]psychologie.uzh.ch (email) http://www.psychologie.uzh.ch/neuropsy/ (website) http://www.juergenhaenggi.ch (private website)
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