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st: generating predicted values for growth models


From   Amy Hsin <hsin.amy@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: generating predicted values for growth models
Date   Fri, 29 Jun 2012 16:03:42 +0200

Hi,

I am trying to generate predicted values from linear growth curves and
am running into problems. The predicted values that I am generating
using models that adjusts for a variety of covariates are the same as
the observed values, which does not make sense. Is there something
that I am obviously doing wrong?

Here is a simplified version of my model.

xi: xtmixed gpach i.wave*race i.wave*female i.wave*psescomk8 if
gpachmiss!=1 || id: wave , cov(unstructured) variance emiterate(250)
mle;
margins, over(race wave);

-gpach are test scores evaluated at time 0, 1, 2 and 3
-race and female are both dichotomous variables
-psescomk8 a time invariant continuous covariate
In this model, I'd like to measure time nonparametrically so I am
including it as a series of dummy variables.
When I use the "margins" command to estimate predicted test scores for
each racial category at each point in time, I get values that are
identical to the observed values.

Any ideas as to what I am doing wrong?

Thank you in advance.


Amy Hsin
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