On Fri, Mar 9, 2012 at 2:44 PM, Chong, Catherine - SJHMC <
[log in to unmask]> wrote:
> Dear Experts,
>
> I am new to SPM, so please excuse my question.
>
> I seek to evaluate a memory paradigm (new versus repeated faces) for a
> patient and a control group of participants. I would like to correlate
> mean cortical thickness values for the hippocampus into my contrast design,
> i.e. my question is: Is hippocampal thickness correlated to fmri brain
> activation patterns? Do I implement the mean cortical thickness values as a
> covariate in my analysis in a 2-sample T-Test?
>
(1) Are you using cortical thickness or hippocampal volume? If you are you
using thickness, is there a reason that you chose thickness?
(2) As for the analysis, there are are couple of approaches.
(a) two-sample t-test with one covariate that is demeaned. This will
give you the covariate-adjusted means. Assumes the slope is the same in
both groups.
(b) two-sample t-test with one covariate. This will give you the group
intercepts. Assumes the slope is the same in both groups.
(c) two-sample t-test with two covariates that is demeaned
within-group. This will give you the group means controlling for the
covariate. You can also test is the slopes are different.
(d) two-sample t-test with two covariates that is demeaned across
everyone. This will give you the covariate-adjusted group means. You can
also test is the slopes are different.
(e) two-sample t-test with two covariates that is not demeaned. This
will give you the covariate-adjusted group intercepts [I believe]. You can
also test is the slopes are different.
Models c-e all have the same slope estimates.
If there is an difference in the slopes, you should not interpret the group
means/intercepts. The average of the slopes might also be difficult to
interpret.
>
> Thank you very much for your help,
> cheers,
> catherine
