I have a repeated measures design and I wish to test if each of four treatments are different at each of the 5 repeated times. I have struggled with the syntax for this test in Stata 11 so I have tried the example from the repeated measures FAQ (dataset t77). Following anova I tested the main effects as follows:
test 1.calib==2.calib
( 1) 1b.calib - 2.calib = 0
F( 1, 12) = 8.99
Prob > F = 0.0111
but when I tried to test the interaction I got
. test 1.calib#1.shape == 2.calib#1.shape
( 1) 1b.calib#1b.shape - 2o.calib#1b.shape = 0 Constraint 1 dropped
F( 0, 12) = .
Prob > F = .
As a consequence I used the wsanova example with the following results:
test 1.calib==2.calib fails with error r(111) however
. test _coef[calib[1]] = _coef[calib[2]]
( 1) calib[1] - calib[2] = 0
F( 1, 12) = 22.30
Prob > F = 0.0005
. test _coef[calib[1]*shape[1]] = _coef[calib[2]*shape[2]]
( 1) shape[1]*calib[1] - shape[2]*calib[2] = 0
F( 1, 12) = 1.69
Prob > F = 0.2186
appears to work but has a different F and p to the anova example for the main effect.
My question is what am I doing wrong or is it not possible to carry out this type of test?
Any advice gratefully received.
Ted
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