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st: Re: Interpretation of contrasts


From   Janet Hill <janethill73@yahoo.co.uk>
To   statalist@hsphsun2.harvard.edu
Subject   st: Re: Interpretation of contrasts
Date   Wed, 13 Feb 2008 13:10:32 +0000 (GMT)

I have a repeated measures anova with 5 repeated time periods and the response measured at 3 stress levels and I am estimating the model as:
wsanova resp time,id(spec) between(stress) eps
test, showorder shows there to be 54 elements in the design matrix.

My problem is that I want to look at time*stress interactions at the last time period. I have constructed a  test matrix for the necessary constraints but I get the following error message:
. test, test(c6)
 ( 1)  time[5]*stress[1] - time[5]*stress[2] = 0
 ( 2)  time[5]*stress[1] - time[5]*stress[3] = 0
 ( 3)  time[5]*stress[2] - time[5]*stress[3] = 0
       Constraint 1 dropped
       Constraint 2 dropped
       Constraint 3 dropped

. test, test(c6) mtest(sidak)
_mtest: 0 valid tests

I can carry out this tests at other time periods.

My question is how can I carry out this particular test. 

Thank you,
Janet





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