There is no single contrast to test. You could do 1 -1 0 and then 0 1
-1 to test the two elements of the contrast. You could also use an
F-test and then post-hoc t-tests to confirm the directions. The F-test
would be: 1 -1 0; 0 1 -1
Your contrast is invalid as 1 row is all zeros and the contrast would
also represent where either Group 1 or Group 3 was different than 0 as
F-contrasts don't have direction.
Hope this helps.
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, Dec 19, 2012 at 9:40 AM, Yoan Mihov <[log in to unmask]> wrote:
> Dear SPM community,
>
> I have an experimental design with three independent groups each receiving
> one of three different treatments. This is expected to decrease activity in
> group A and increase activity in group C, as compared to placebo (group B).
> How can I incorporate this hypothesis in a single model on the second level?
> Would the solution be anything close to a design matrix like the following
> one:
>
> -1 0 0
> 0 0 0
> 0 0 1
>
> Many thanks in advance for all answers and hints!
> Yoan
>
> --
> Yoan Mihov, Dipl.-Psych.
> NEMO Research Group
> Department of Psychiatry
> University of Bonn
> Sigmund-Freud-Str. 25
> 53105 Bonn
> Germany
> Tel.: +49 (0)228 287 11165
> web
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