Hi,
no - you can't pass F-contrasts to higher levels directly. Passing
VARCOPEs up to a group level is based on t-test contrasts - the group
stats framework cannot deal with passing up of f-test contrasts as not all
of the assumptions would stand.
However, you use the COPEs of the lower level F-test (i.e. the COPEs that
go into the lower lvel F-test) and then do an F-test at the higher level.
You may also consider using a type of summary stats of your COPEs of
interest, i.e. the root-mean-squared (RMS) of the COPEs, and pass them up
to the higher level using randomise.
Cheers,
Andreas
Am 30.07.15 16:19 schrieb "FSL - FMRIB's Software Library on behalf of
Esther Heckendorf" unter <[log in to unmask] on behalf of
[log in to unmask]>:
>Hi,
>
>We have a small question about using an F-test in FEAT. We've shown
>participants three different types of stimuli (S1, S2 and S3) and would
>like to test the main effect of stimulus type. We have no specific
>hypotheses regarding the direction of effects. In the lower level
>analysis we have included contrasts comparing each pair of stimuli (i.e.,
>S1 vs S2, S1 vs S3, and S2 vs S3), as well as an F-test across two of
>these contrasts (S1 vs S2 and S2 vs S3) to test the 'entire' main effect
>in one test. When setting up a higher level analysis to test the
>significance of the effects in the entire group of subjects we could only
>include the contrasts comparing each pair, but not the F-test. That's of
>course a bit of a problem, as we would like to check the significance of
>the 'entire' main effect before performing individual comparisons. Is it
>possible to include the F-test in the higher level analysis somehow?
>
>Thanks!
>Esther
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