Hi Steve-
Thank you so much for your speedy reply. I was wondering if you (or any of
the FSL people) could clarify what type of statistic is calculated for the
contrasts when covariates are included in the model. I ask this because when
I ran an unpaired T-test and calculated the patients>controls contrast and
controls>patients contrast, the result was similar, but not exactly the
same, as the result I obtained for the contrast I described in my previous
message (sex and age as covariates, but not included in the contrast). So,
to clarify, here is the original "contrast" (scenario 1) and the t-test
(scenario 2):
SCENARIO 1:
Group control patient age sex
1 1 0 21 1
1 1 0 24 -1
1 1 0 35 -1
1 1 0 42 1
1 0 1 23 1
1 0 1 43 -1
1 0 1 22 1
Contrast control patient age sex
ctrl>pat 1 -1 0 0
pat>ctrl -1 1 0 0
avg ctrl 1 0 0 0
avg pat 0 1 0 0
SCENARIO 2 (age and sex covariates removed from the model)
Group control patient
1 1 0
1 1 0
1 1 0
1 1 0
1 0 1
1 0 1
1 0 1
Contrast control patient
ctrl>pat 1 -1
pat>ctrl -1 1
avg ctrl 1 0
avg pat 0 1
Could you explain whether (and how) age and sex are included in the model
when I calculate a contrast (without an F test), and why this would or would
not be the same as performing a T-test without these covariates?
Thank you again for your time. Your help is truly appreciated!
Liberty
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