afni.nimh.nih.gov

Hi Prerona,

This should not affect the significance of any results
(since it is constant scalar across all subjects, unless
it is unbalanced, like A+B+C-D-E), but it is often nice
to make contrasts of unit weight in the positive and
negative directions.

So for a simple A-B contrast -expr a-b is good. But
for a contrast of ((A-B) - (C-D)), it might be better to
divide by 2, since this ends up as (A+D) - (B+C), and
each has a weight of 2. So for that, consider
-expr '(a+d)/2-(b+c)/2'.

- rick