Hi FSL Guru's
I've painted myself into a really complicated repeated measures,
nested design, and I'd appreciate some feedback about whether the
EV's and contrasts I've set up for my second level analysis are
correct.
This is a dual-task task visual attention study, so we have each
of the dual task conditions in a single task form. Because we
have some repeated measures within the dual task condition,
however, we end up with an unbalanced (nested design).
The conditions are
A (single task)
1 center task
2 peripheral vision task, proximal to fixation
3 peripheral vision task, distal to fixation
B (dual task)
1 center task + proximal peripheral task
2 center task + distal peripheral task
I've set up my matrix using dummy variables, such that
X1 = 1 single, 0 else
X2 = 1 center single, 0 else
X3 = 1 proximal peripheral single, 0 else
X4 = 1 proximal dual single, 0 else
X5 = subject 1
X6 = subject 2
X7 = subject 3
The EV Matrix ends up being
A1 1 1 0 0 1 0 0
A2 1 0 1 0 1 0 0
A3 1 0 0 0 1 0 0
A4 0 0 0 1 1 0 0
A5 0 0 0 0 1 0 0
And my contrasts are structured
single task 1 0 0 0 0 0 0
dual task 0 0 0 .5 .165 .165 .165
center single 0 1 0 0 0 0 0
etc.
My biggest concern is that my EV's are set up using a very simple
"on/off" matrix, but if I set it up in the more traditional manner
(i.e. 1 for single task, -1 for dual task) I find I can't make the
maths work out for the contrasts I need. (I'll be happy to accept
feedback about any errors, however).
Thanks in advance for any help you can give.
Paige
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