Hello Everyone,
Thank you all for your replies. We converted the values into -log10(p) and
accounted for two-tailed, but the values were still off, and they are not even
off in any consistent pattern. For example:
FS: .1541 .1109 .0749 .0641 .0514 .0281 .0182 .0141 .0132
.0025 .0007 .0006
SAS: .3226 .0852 .2131 .0818 .0760 .2425 .6196 .0020 .0458
.0039 .0003 .0020
Our SAS program only gives output to four digits. Could the discrepencies be
coming from rounding errors?
Mahalo,
Jeff
> Date: Mon, 8 Jun 2009 19:21:53 -0400
> From: gr...@nmr.mgh.harvard.edu
> To: ni...@nmr.mgh.harvard.edu
> CC: jsad...@hotmail.com; freesurfer@nmr.mgh.harvard.edu
> Subject: Re: [Freesurfer] mri_glmfit significiance verification outside
> freesurfer
>
> Also, p-values for t-tests are two-sided.
>
> Nick Schmansky wrote:
> > Jeff,
> >
> > sig.mgh actually stores the -log10(p), not p, so to get the true p-value
> > of say, -2 (in the sig.mgh), take 10^-2 (giving you the true p-value of
> > 0.01).
> >
> > Nick
> >
> >
> > On Mon, 2009-06-08 at 16:48 -0600, Jeff Sadino wrote:
> >
> >> Hello Surfers,
> >>
> >> I am trying to verify the p-value sig.mgh maps outputted from the
> >> mri_glmfit command as the first part of a more advanced analysis. We
> >> have been extracting the thickness data for a single vertex from each
> >> of our 58 subjects in two control groups and then running a
> >> significiance analysis is SAS. We thought that the output from SAS
> >> should match the p-value in the sig.mgh file, but the p-values do not
> >> match at all. We have tested multiple data points. Does freesurfer
> >> do some sort of a more advanced significance analysis that is not in
> >> the standard documentation?
> >>
> >> Thank you very much,
> >> Jeff Sadino
> >>
> >>
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>
> --
> Douglas N. Greve, Ph.D.
> MGH-NMR Center
> gr...@nmr.mgh.harvard.edu
> Phone Number: 617-724-2358
> Fax: 617-726-7422
>
> In order to help us help you, please follow the steps in:
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>
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