On Fri, 24 Jun 2005 08:25:15 -0500, Glabus, Michael <[log in to unmask]>
wrote:
>Dear SPMers
>
>We are running an experiment that requires subjects to verbally report at
>the end of a session, rather than use a button-press.
>
>We have three conditions: Task A (A), Task B (B), and rest (R).
>
>The experiment is organised in six sessions, e.g,
>
>R A; R B; R A; R B; R A; R B. (randomized across subjects)
When you write
R A
do you mean one long R block followed by one long A block, and that's it?
Or do you mean "this session has R blocks and A blocks, alternating".
Problem with the former is that difference between R and A is confounded
with slow drift.
Cheers,
S
>I appreciate that it would have been better to have all conditions in each
>session,
>but this would not allow us to properly address our specific aims.
>
>I don't think we can contrast the main effects of interest at the first
>level, so
>to examine the A v B conditions, would it be better to do this at the
second
>level, i.e.,
>using the A v R and B v R contrasts?
>
>Regards - MFG
>
>
>
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