Hi
Thank you for your help.
I did not mean F is a bug. I meant defining t-contrast [-1 -1 2] or [-1 -1
1] worked well before. Now it does not. I can define t-contrast, however,
with two columns (e.g.: [-1 0 1]), but with three I cannot.
I know these other opportunities (f-test, conjunction). I am just curious
what is the problem with this kind of t-contrast I want to use.
Best,
Auer, Tibor M.D.
PhD-student
University of Pécs, Medical Faculty
Department of Neurosurgery
Rét u. 2, Pécs, H-7623, Hungary
Tel.: +36-20-986-9341
E-mail: [log in to unmask]
-----Original Message-----
From: cyril pernet [mailto:[log in to unmask]]
Sent: Wednesday, May 30, 2007 4:41 PM
To: Auer, Tibor MD.; SPM
Subject: Re: [SPM] using t-contrast in ANOVA
Hi there,
>
> Dear SPM-ers,
>
> I have set up an ANOVA-design with three levels (see Design Matrix
> attached), and I try to calculate a T-contrast to "substract" the
> fisrt two levels from the third [-1 -1 2].
>
> With former revision of spm worked well, but now it says 'trying to
> define a t that looks like an F'.
>
> Is it a bug, or did I something wrong?
>
Not sure but I guess it a feature :-)
Unless you have strong hypothesis on the effect size of the col 3 (col3
> than average col1 and col2) you would perform an F like [-1 0 1; 0 -1
1] which tests if col3 is > col1 and/or col2 - or if you want even
stronger do [-1 0 1] and [0 -1 1] and perform a conjunction null =
col3>col1 AND col3>col2
Hope this helps
cyril
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