dear list.
i am struggling with the flexible factorial design for a while and found
the discussion on the list very helpful. i still got problems with creating
the contrasts in my design. so if one of the experts got the time to look
over my contrasts and give me some further advice it would be very helpful.
my design is as follows:
2 groups (N1, N2), 2 conditions (C1, C2). i specified 3 factors (subject,
group, condition) and got a design matrix comparable to darrens and matts
one (see attached file). the first 26 columns are for the subjects, the
last 4 columns are for the factor interactions (N1xC1, N1xC2, N2xC1, N2xC2).
so i want to have the following contrasts, which i managed to specify in
spm. are they correct?
main effect of group (N1 > N2) =
2*1/N1*ones (1,N1) 2*1/N2*-ones (1,N2) 1 1 -1 -1
(because of group differences i have to include the rank deficient subjects
columns, right?)
main effect of condition (C2 > C1) =
zeros (1,N1+N2) -1 1 -1 1
(no group effect, no subject columns necessary???)
group difference condition1 (C2 > C1) =
1*1/N1*ones (1,N1) 1*1/N2*-ones (1,N2) 1 0 -1 0
(group effect so subject columns included, just 1 condition therefore only
1 as multiplicator ???)
main effect conditions for group 1 (similar to one sample t-test????) =
2*1/N1*ones (1,N1) zeros (1,N2) 1 1 0 0
(subject columns have to be included, but why???)
what i did not manage to define is the interaction of the factor group and
condition.
2*1/N1*ones (1,N1) 2*1/N2*-ones (1,N2) 1 -1 -1 1 gives an invalid contrast
warning.
furthermore i failed to design the contrast of C1 < C2 for group 1 (or
group 2).
if one of the experts could give me advice would be great.
thanks a lot
markus
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