Hi,
I have a question about ANOVA analysis in FEAT.
I have just run a 2x2 ANOVA on my data (two factors, both repeated
measures and with two levels). The inputs were 76 cope files (19 subjects x 4
levels), derived from the first and second level GLM (within subjects). I
specified the design matrix as suggested in the 2x2 example on the website,
but replaced EV4 with 19 subject-specific EVs. This gave me a total 22 EVs. I
chose mixed effects modelling and requested three F-tests, for the two main
effects and the interaction effect. As suggested in the web example, I divided
the output fstat images of the two main effects by the fstat image of the
interaction effect, and then converted these to zfstat images.
Is this the correct way to do it?
The reason I ask is that the results are quite different from what I expected,
based on the standard GLM analysis (pairwise comparisons). For example, the
standard analysis shows a large difference between the two levels of factor A
(A1>A2), but the ANOVA shows no main effect of factor A. The two zfstat
images look a bit odd, they contain scatters of single voxels, and clusters
appear only with z 0-1.5. The original zfstat images look more "normal", and in
line with my predictions, as does the zfstat image of the interaction effect.
If anyone knows whether and where I went wrong, please let me know.
Thanks in advance!
Hanne
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