At 22:19 13/02/2008, you wrote:
>Hi Yvonne,
>
>Since no one more statistically savvy than me has answered as yet,
>I'll poke my head out and say "no" -- FSL doesn't offer an
>implementation of the "minimum statistic" implementation of
>conjunction analyses. To be honest, though, there are real problems
>with interpreting those statistic values, as pointed out by Tom
>Nichols and colleagues. In many cases it is sufficient to use
>inclusive masking. If the contrasts are truly orthogonal, then you
>can reasonably multiply the p-values together to get a "conjunction"
>p-value in a given voxel. For instance, if you were interested in
>areas in Group 1 where A>B and masked it with Group 2's A>B (at
>p<0.001 uncorrected to pick a random threshold...), then any areas
>at p<0.001 in the G1 A>B contrast that are also present in G2 A>B
>are unlikely to be there by chance given that the corresponding
>p-value would be p<10^-6.
>
>Personally, I wouldn't feel the need to see a computed p-value -- it
>would be sufficient to know that the "conjunction" contrasts were
>truly orthogonal and know the level that each one was
thresholded at.
Sorry -- my email pulled a fast one on me!
Joe
------------------
Joseph T. Devlin, Ph. D.
Dept. of Psychology, UCL
Gower Street
London, WC1E 6BT, UK
email: [log in to unmask]
|