Dear all,
I would like to have your opinion regarding a 2nd level design (flexible
factorial) I built, which includes 2 groups (patients - controls) and 8
conditions (4 tasks x 2 emotions) measured per group.
The model uses 3 factors: subject, group and condition. It models the
main effect of group and conditions, as well as the group-by-condition
interaction.This is actually the design2 from the Glasher & Gitelman
tutorial, you can see what the matrix looks like in the attached file.
My question is the following: is it valid in this kind of model to test
for the effect of a contrast between 2 conditions (ex A1A2 > B1B2) in
*one group only*?
I know how to built a test for a single condition in one group (contrast
6 from design2 of the tutorial), but for a *contrast* the interface
won't allow it. Then: is it statistically valid ?
This question extends to other flexible factorial models used for
instance to model RM anova with a single group.
I know we can do it, but is it statistically valid to estimate simple
main effectsin such a model (and weight the non used conditions of the
design with zeros) or shall we always use all conditions of the design
in the contrasts we estimate (and build ttest instead to estimate simple
main effects or simple comparisons between two conditions) ?
Thanks for your input !
Camille Piguet
--
MD-PhD student
Laboratory for Neurology and Imaging of Cognition
Department of Neurosciences, Faculty of Medicine
University of Geneva
Centre Médical Universitaire
1 rue Michel-Servet
1211 Geneva, Switzerland
+41.22.379.53.24
http://labnic.unige.ch
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