st: Comparing coefficient across two xtmixed (growth curve) models

[Lance Erickson <lance_erickson@byu.edu>]

I am working with a panel dataset that has 4 measurement periods and estimating a mixed (growth curve) model using -xtmixed- where the dependent variable is nested within individuals. I want to compare a coefficient across two models where the only difference between the models is the introduction of an additional level-2 predictor. For example, the two models are specified like this...

xtmixed y age x1    || id: age, cov(un)
xtmixed y age x1 x2 || id: age, cov(un)

Specifically, I want to test whether the estimate of x1 from the first model is significantly different than the estimate of x1 from the second model. I know I could 'eyeball' the difference but would feel better about interpreting them if there was a formal test.

I understand that -suest- will not work in this situation because -predict- does not allow the -score- option after -xtmixed-. I haven't found a solution after various attempts at finding the answer through the statalist archives and alternative internet sources. 

Any direction or clues would be much appreciated.

Thanks for considering the question,

Lance


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