Dear list,
I know questions related to mine have already been posted, but I couldn't
find an answer to this specific one:
Suppose I have an experiment with 10 subject and 4 conditions (A, B, C, D)
and I want to test the conjunction of A-B and C-D. If I enter this in SPM,
I get a t-statistic with 18 df, suggesting that SPM treats each of the 20
first level contrasts (ie, the A-B and C-D contrasts) as coming from a
different subject.
My questions: Is this interpretation correct? If so, is this assumption
necessary because a minimum-t distribution (as used when testing against
the global null) requires its component t-distributed variables to be
independent?
Thanks in advance
Tom
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