Hi Steve,
I would like to return to the question I presented earlier. Your reply answers
to my question about group level analysis. Thank you. However, if I want to
compare results of an individual subject in pre- and posttreatment conditions,
how do I accomplish this correctly with FSL?
- Antti Korvenoja
Quoting Stephen Smith <[log in to unmask]>:
> Hi.
>
> > I would like to ask a question about setting up analysis of a
> follow-up study in
> > FSL. I would have two blocked baseline-stimulation sessions separated
> by a
> > treatment. I would like to test for differences between activation in
> > pre-treatment an post-treatment sessions and perform this both on
> individual and
> > group level.
> >
> > I presume that using the treatment as on explanatory variable would
> not be
> > sufficient, since global differences between sessions would be modeled
> by this
> > variable. So far I have not found any hints in the documentation. I
> tried to
> > search the SPM mailing list but without success.
> > -Antti Korvenoja
>
> if you have just two sessions, one before and one after treatment, then
> you want to carry out a fixed-effects analysis to comtrast the two
> sessions' results.
>
> to group analysis in FEAT in general is easy - however, because you want
> here to compare a single session with another single session, which
> FEAT group stats doesn't like too much, you will need the following
> workaround (this will give you a totally valid fixed effects analysis -
> note that this kind of thing will be even easier in the next version of
> FSL, due out early next year):
>
> Run FEAT on session A, including registration.
>
> Run FEAT on session B, including registration, but with negative values
> for the contrasts (eg change 1 to -1 in the contrast setup).
>
> Do group FEAT (advanced->no first level analysis) and just enter the two
> FEAT sessions and analyse as a single group (i.e. leave the number in
> group "A" at zero). your fixed effects analysis will give you what you
> want.
>
>
> Thanks, Steve.
>
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Antti Korvenoja
Dept. of Radiology & BioMag Laboratory, Helsinki University Central Hospital
Biomedicum Helsinki, P.O. Box 700, FIN-00029 HUS, Finland
tel:+358-9-471 71786 * gsm:+358-40-7498469 * fax:+358-9-471 75781
[log in to unmask] * http://www.helsinki.fi/~akorveno/
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