(1) If you include a column for each subject in a one-sample t-test,
then the group effect will always have a t-statistic of Inf. This
results from the residual being 0. As far as I know, this was never
done in SPM5.
(2) I do not have a strong opinion on this, except to say that your
contrast will no longer be comparing TaskA v. TaskB or TaskA v.
baseline. Rather, you will be comparing the globally-adjusted
contrast.
(3) What subject-specific are you referring to?
From the wording in your email, it seems like you might be using
multiple measurements per subject. In this case, you should not be
using a one-sample t-test.
Best Regards, Donald McLaren
=================
D.G. McLaren, Ph.D.
Postdoctoral Research Fellow, GRECC, Bedford VA
Research Fellow, Department of Neurology, Massachusetts General Hospital and
Harvard Medical School
Website: http://www.martinos.org/~mclaren
Office: (773) 406-2464
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On Fri, Apr 27, 2012 at 6:43 AM, Richard Morris
<[log in to unmask]> wrote:
> Dear list,
>
> I've noticed a change in the one-sample t-test design matrices produced by SPM8 compared to SPM5. I seem to remember SPM5 used to (automagically?) include subject effects, with columns for each subject in the design matrix, but SPM8 doesn't do that anymore. Is there a setting change I can make to reintroduce subject effects in my design matrix?
>
> On a related note, is there any reason not to include the global covariate (ANCOVA) in a one-sample t-test of fMRI data? I've noticed I often get more regionally specific activation with higher t-values in my results when I include the global covariate. I'm guessing this is because of subject-specific effects which I would like to remove/minimise.
>
> Best,
>
> Rich
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