Auer, Tibor MD. wrote:
> spm_SpUtil gave back: "true". Does it means OK?
It means the contrast is estimable, which means that Jacqueline's and
Cyril's suggestions that the contrast weights should be changed in
some way (e.g. summing to zero, or being scaled in some way) are not
likely to be the explanations. I'm afraid I'm not sure what might be
though...
I've searched the code for that error message, and it comes from
spm_FcUtil. The distinguishing feature of F-contrasts (aside from
SPM's restriction to right-tailed T-contrasts) is that they are
matrices rather than vectors. And indeed, if I try the following:
X = kron(eye(3),ones(4,1)); % an example ANOVA design matrix
c = [-1 -1 2]'; % vector T-contrast
K = [-1 -1 2; 1 -1 0]'; % matrix F-contrast
spm_FcUtil('Set', 'test', 'T', 'c', c, X)
spm_FcUtil('Set', 'test', 'F', 'c', K, X)
spm_FcUtil('Set', 'test', 'T', 'c', K, X)
the first two (c as a T-contrast, and K as an F-contrast) work fine,
while the third (K attempting to be a T-contrast) reproduces your error.
This doesn't explain why you seem to get the error for a valid
T-contrast of [-1 -1 2] but it does suggest that you should very
carefully check that you have indeed entered this correctly.
You might also want to investigate something like:
load SPM.mat
X = SPM.xX.X;
N = numel(SPM.xCon);
for n = 1:N
c = SPM.xCon(n).c % looks like your contrast??
spm_FcUtil('Set', 'test', 'T', 'c', c, X)
end
I hope that helps,
Ged.
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