Hi Robin,
> Ah. So f-test results for the ps-plots, then. Great. Let me make sure I
> understand -- I can model using 5 gamma basis functions and do an
> f-test across all five, which gives me one map that is the best fit
> linear combination of all basis functions. (How do I know the weighting
> of each?)
Yep, that's right. You can get a feel for the relative weightings by
looking to see how strongly each individual one fits in the partial model
fits on the right side of the web page. You can get the exact relative
values by extracting the relevant voxel values from the relevant pe?.hdr
image.
> But this brings up another question. I have read in past postings that
> f-test results can not be used in higher level analysis. Does this mean
> that in order to do higher level stats, I must use only for example the
> first basis function?
You can run f-tests at higher level, for example by feeding up 5 basis
function EVs into higher level and setting up an f at higher level. But
what you can't do yet (because it doesn't work within the existing
mathetmatical framework) is pass up f-stats from the lower level up to
higher level. That would be nice because then (for example) you wouldnt be
enforcing the same balance across the different basis functions in
different subjects. What you get at the moment would be (for example) the
best _average_ balance across the basis functions across subjects if you
run the f-test at higher level.
Cheers, Steve.
Stephen M. Smith DPhil
Associate Director, FMRIB and Analysis Research Coordinator
Oxford University Centre for Functional MRI of the Brain
John Radcliffe Hospital, Headington, Oxford OX3 9DU, UK
+44 (0) 1865 222726 (fax 222717)
[log in to unmask] http://www.fmrib.ox.ac.uk/~steve
|