ANCOVA -- "This option is only used for PET data"
The ANCOVA option basically creates a covariate with a global value
for each subject and then splits it by group. You could do something
similar with your vol covariate with out using the ANCOVA. It should
be noted that technically, the model is an ANCOVA even with out saying
yes as you have covariates in the ANOVA framework.
Here is an excellent guide to interpreting your effects in the
presence of covariates: http://mumford.fmripower.org/mean_centering/
In summary, depending on how you center your covariates, the meaning
of the group difference changes.
Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Postdoctoral Research Fellow, GRECC, Bedford VA
Website: http://www.martinos.org/~mclaren
Office: (773) 406-2464
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On Wed, Oct 31, 2012 at 11:26 AM, Gabriel Go.Es. <[log in to unmask]> wrote:
>
>
> Dear SPM experts,
>
> I have design two models into spm8 for an ancova. both are exactly the same
> but (2 groups and 3 covariates), in the first one I choose ANCOVA = "NO",
> and the second one I'd choose "YES", and the results are so different, The
> first one actually show no results at all, and the second model (ANCOVA=YES)
> have some results, even after multiple comparisons correction.
>
> My questions are: Which would be the correct way to interpret my results if
> I use the 2nd model?,
> and what's the difference, when I choose ANCOVA="YES" against ANCOVA ="NO"?
>
>
> Many thanks in advanced,
> Gabriel.
>
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