Dear FreeSurfer Mailing List,
I have a sample of schizophrenia and control subjects for whom I have
run a case-control analysis of cortical thickness using two separate
methods (GLM vertex-wise analysis in freesurfer, repeated measures
ANCOVA analysis of parcellated data in SPSS). However, for each methods
of analysis I am getting extremely different results. For the GLM in
Freesurfer I have only 1 small cluster in the frontal lobe that differs
between cases and controls (controlling for all other IVs, FWMH = 10mm,
cluster-forming threshold= .05, cluster-wise pval=.05), while for the
ANCOVA method all but 8 of the parcellated regions differ significantly
between groups (p<.05). For both methods I have used the same model of
predictors (independent variables = gender, group, scanning site;
covariate = age) and exactly the same sample of participants. I have
also replicated the GLM analysis using the QDEC GUI to ensure that I had
no made any mistakes.
Can you provide any insight into why I would be seeing such different
results for each method using the same data set? My findings using the
ANCOVA analysis make much more sense to me, given previous findings of
reduced cortical thickness in schizophrenia subjects. I was surprised
not to find the same pattern of effects using the GLM analysis.
--
Kind regards,
Bronwyn Overs
Research Assistant
Neuroscience Research Australia
Neuroscience Research Australia
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