Hi again
Couple of corrections to my last email.
The tstat should have been the COPE / sqrt(VARCOPE), and not
COPE/VARCOPE.
but, actually, you don't have to compute this value, as ttoz
takes COPE and VARCOPE as input, and not the t-score.
so you can just do something like
ttoz -zout diffZ diffVARCOPE diffCOPE DOF
sorry for the confusion
Tim
-------------------------------------------------------------------------------
Tim Behrens
Centre for Functional MRI of the Brain
The John Radcliffe Hospital
Headley Way Oxford OX3 9DU
Oxford University
Work 01865 222782
Mobile 07980 884537
-------------------------------------------------------------------------------
On Fri, 6 Jun 2003, Tim Behrens wrote:
> Dear Antti -
>
> I think what you want to do is exactly the same as a fixed effects
> comparison. Feat3 doesn't have an explicit fe analysis in the
> GUI, but in this case you can easily create one with avwmaths
>
> You have COPEs and varCOPEs from before and after the treatment:
>
> form the difference image of the COPEs:
>
> avwmaths postCOPE -sub preCOPE diffCOPE
>
>
> to get the FE variance for this new cope do
>
> avwmaths postVARCOPE -add preVARCOPE -div 4 diffVARCOPE
>
> to get your t-scores do
>
> avwmaths diffCOPE -div diffVARCOPE diff_TSTAT
>
> your "degrees of freedom" is the sum of the DOFs of the first two expts.
>
>
> you can then run ttoz to get zscores
>
>
> Hope this helps
>
> Cheers
>
> Tim
>
>
>
>
> On Fri, 6 Jun 2003, Antti Korvenoja wrote:
>
> > Hi!
> > It is unclear to me what is the correct way within current FSL to make a
> > comparison between activations in a session before some treatment and after
> > the treatment on invidual level. I understand the paired t-test (as in FSL
> > document example) would be applied if one wishes to get the group level
> > differences. In some situations individual level differences might be of
> > interest. I would very much appreciate help in finding out how to do this
> > kind of analysis correctly with FSL.
> >
> > -Antti
> > --
> > Antti Korvenoja
> > Biomedicum Helsinki, Radiology
> > P.O. Box 700, 00029 HUS
> > Finland
> >
> > tel: +358-9-47171786 : mobile: +358-40-7498469
> >
>
> --
> -------------------------------------------------------------------------------
> Tim Behrens
> Centre for Functional MRI of the Brain
> The John Radcliffe Hospital
> Headley Way Oxford OX3 9DU
> Oxford University
> Work 01865 222782
> Mobile 07980 884537
> -------------------------------------------------------------------------------
>
>
>
>
>
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