Hi Robin,
On Tue, 27 Sep 2005, Robin Goldman wrote:
> Hi there,
>
> Perhaps a basic question about setting up contrasts, but I'm confused.
>
> I have, for example, 3 conditions A, B, and C, one ev for each. B is a repeat presentation of A, but I
> broke them appart to be able to probe differnces to repeats. I would like to perform the following
> contrasts --
>
> A + B
>
> (A + B) - C
>
> The first, I assume, is just 1 1 0. I also assume this would be the same as having had 2 evs, the
> first ev = A+B with the contrast 1 0. Is this true?
Nearly. The [1 1 0] COPE value is the same as the [1 0] PE in the 2 EV
case, but in the 3 EV model the residuals will be lower so the Z higher.
> As for the second contrast, is it 1 1 -1 or 1 1 -2?
Yep: [.5 .5 -1] i.e. [1 1 -2]
Cheers.
>
> thanks!
> R
>
--
Stephen M. Smith DPhil
Associate Director, FMRIB and Analysis Research Coordinator
Oxford University Centre for Functional MRI of the Brain
John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
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