Hi,
you could try including average cortical thickness over the entire
hemisphere as a covariate. This was Mike Harms' suggestion, and I think a good one.
why is it a good one? for cortical thickness: i'm not so sure. my 2 cents (and i may be wrong!): - controlling for intracranial volume is done to remove differences due to overall size variability. - the relationship between thickness and size is much less strong than between volume and size (or surface and size). - suppose your groups differ in mean thickness, if you would like to include mean thickness as a covariate in a mapping study (vertex-wise comparisons) of cortical thickness you would have to show that the group-difference in mean thickness is due to an effect that's spread out over the whole cortex (an overall effect, not localized), otherwise the mean thickness covariate is not a good estimator of the overall size factor that you'd like to remove.
check Peter Kochunov's recent publications on this.
-joost
cheers
Bruce
On Thu, 8 Apr 2010, Liukarl wrote:
Hello, Freesurfer experts:
I noticed for analyzing the results from autorecon2, the intracranial volume are controlled as covariate in some publications. Is there any corresponding covariate for cortical results from autorecon3, cortical thickness, surface, and volume?
In my current study, there are two group: one is a group with less optimal developmental environment and the other is control. I noticed that without any covariate, the r square from cortical measure and group variable was really low, only accounting for 2%. Is any standard way to analyze the cortical data?
Thanks!
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