Hi all,
To Jacqueline,
Theoretically you may be right. I am not an expert. What I said, It had
worked previously.
To Ged,
I use the same revision (748).
I have tried what you suggested: It looks well, like a 3-level ANOVA (3 by 3
"checkboard"):
100
010
001
spm_SpUtil gave back: "true". Does it means OK?
Best,
Tibor
-----Original Message-----
From: Ged Ridgway [mailto:[log in to unmask]]
Sent: Wednesday, May 30, 2007 5:37 PM
To: Auer, Tibor MD.
Cc: [log in to unmask]
Subject: Re: [SPM] using t-contrast in ANOVA
Hi Tibor,
What version and revision of SPM are you using? (the latest release is
SPM5 rev 748)
I'd suggest looking at your design matrix, either with the GUI Review
option or go into the directory with the saved SPM.mat, and do:
load SPM.mat
X = SPM.xX.X;
then play around, e.g. does the design look alright:
imagesc(X);
and are your contrasts estimable:
c = [-1 -1 2];
spm_SpUtil('isCon', X, c')
Hope that helps,
Ged
Auer, Tibor MD. wrote:
> Hi,
> It does not work, too.
>
> Former, using [-1 -1 1] worked also well.
>
> Best
> Auer, Tibor
>
> -----Original Message-----
> From: Jacqueline Griego [mailto:[log in to unmask]]
> Sent: Wednesday, May 30, 2007 5:09 PM
> To: [log in to unmask]
> Subject: Re: [SPM] using t-contrast in ANOVA
>
> Hi, I had a similar problem and maybe this will help yours--for some
> reason SPM would only take it defined as [-.5 -.5 1]
> Cheers
>>>> "Auer, Tibor MD." <[log in to unmask]> wrote on 5/30/2007 11:05
> AM:
>> 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
>
>
> Jacqueline Griego, PhD
> MPRC
> Functional Neuroimaging Lab
> PO Box 21247
> Baltimore, MD 21228
>
> Phone: 410.402.6030
> FAX: 410.402.6077
> [log in to unmask]
>
|