[MINC-users] t threshold for corrected p value of Aston's method

[Andrew Janke]

Hi Ji,

I was hoping Sylvain would answer this one as I am not that familiar
with the stats associated with PET but in any case here goes...


2008/5/1 Ji Hyum KO <kojinet at bic.mni.mcgill.ca>:
>  As far as I understand, I should calculate the t threshold based on
>  Worsely et al., Human Brain Mapping, 1996.
>  I am really sure that it is very well-written famous paper, but I
>  couldn't figure out how to calculate the t-threshold in the given
>  conditions.

Correct, to calculate this I would suggest that you use Keith Worsleys
MATLAB package (called fmristat) to do this.

   http://www.math.mcgill.ca/keith/fmristat/

>  Is there any easy way to calculate t threshold for p<0.05 (corrected)?

This will depend on the number of subjects, (and thus Degrees of
Freedom), the number of voxels you are considering and so forth.

>  And, is it going to be the same even if I consider the whole brain rather
>  than just striatum, e.g., fallypride study?

It will be different, but again this will depend on the method you use
to calculate the t-value. Certainly it will change if you calculate
pooled variance across you data (or mask).

Again though I would suggest that you spend some time getting
acquainted with the fmristat package. Keith has a number of examples
on his webpages that should help you get going.


a

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Andrew Janke (a.janke at gmail.com || http://a.janke.googlepages.com/)
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