Dear SPMers,
I think I have now read all the threads on conjunction analysis, but I
am still unsure how to set it up properly. I tried all constellations
and results vary a lot. First of all, I'd like to use the "global" null
option as offered by SPM, because the "conjunction" option will be to
conservative for my data (including similar options that use imcalc to
compute common regions/ overlaps).
The correct way for one group of subjects that underwent several
conditions seems to use a 2nd level one-way ANOVA (not the
within-subject one) and to do the proper adjustments for sphericity.
However I am not sure on sphericity. Levels of the factor are probably
dependent, so is it correct to set the independence option
(stats.factorial_design.des.anova.dept = ) to NO (= 1)? I am even less
sure about the variance option
(stats.factorial_design.des.anova.variance =), and this even seems to be
more critical. What would be the appropriate setting here? My data look
nice if I use equal variance, and less expected if I use unequal variance.
What is the analoguous way to set this up for two groups of subjects
that underwent the same, say 4, conditions. Ideally, I'd like to obtain
SPMs for both groups separately and then also the group comparison for
the conjunction. I think I know how to define all the contrasts needed,
but again I do not know how to properly set up the model. Use of
full-factorial or flexible factorial? What independence and variance
options should be applied to the group and condition factors?
Any help is highly appreciated.
Thank you,
Jens
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Jens Kronschnabel, Ph.D. student
Department of Child and Adolescent Psychiatry, University of Zurich
Neumünsterallee 9, CH-8032 Zürich, Switzerland
+41 43 499 2650
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