Yes.
Doug Greve wrote:
But while an F with J=1 gives the same p value as an unsighed t, the
actual statistic will be F = t^2. Could this account for the discrepancy?
Glenn Lawyer wrote:
No, not at all sure. That is why I am asking. However, mri_glmfit
says that the values should be t-values if there is only one row in
the contrast matrix:
"The F-ratio for the contrast is then given by:
F = G'*inv(C*inv(X'W'*W*X))*C')*G/(J*rvar)
The F is then used to compute a p-value. Note that when J=1, this
reduces to a two-tailed t-test."
In my test data, J does equal 1.
Don Hagler wrote:
Are you sure that it is saving t-values in F.mgh and not F-stats?
From: Glenn Lawyer <[EMAIL PROTECTED]>
<mailto:[EMAIL PROTECTED]>
To: freesurfer@nmr.mgh.harvard.edu
<mailto:freesurfer@nmr.mgh.harvard.edu>
Subject: [Freesurfer] t-value saved values
Date: Thu, 20 Sep 2007 15:00:44 +0200
Hi,
I asked about this last week, and had a nice discussion with Doug,
but somehow in that we never got the answer to my original question.
When FreeSurfer saves t-values (in F.mgh), what is it actually
saving? The numbers in the file do not have a t-distribution (even
when the source data for the glm is random noise). Is a transform
applied to the t-values before the write, as is done with the
p-values?
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MGH-NMR Center
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In order to help us help you, please follow the steps in:
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+ +352 661 967 244 +
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+ Seksjon Vinderen +
+ PB 85 Vinderen +
+ 0319 Oslo +
+ http://folk.uio.no/davidgl +
+++++++++++++++++++++++++++++++++++:)
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