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st: cross-classified random effect model with xtmelogit


From   Mrs Helda Khusun <helda.khusun@uqconnect.edu.au>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   st: cross-classified random effect model with xtmelogit
Date   Mon, 8 Mar 2010 01:23:37 +0000

Dear satalister,

I am trying to fir a cross-classified random effect model for estimation of age, period and cohort effect of a longitudinal data, in which age are nested and cross-classified in time of survey and birth cohort. The outcome is whether or not a person is overweight. Each person is followed longitudinally and measured at three time periods.

Initially I used the following syntax:

. xtmelogit overwt0 agetrc year0 bcohdum ||_all:R.year0||bcohdum:||pidlink: if s_analysis==1, laplace

where: overweight is the outcome (0/1), agetrc(age, continuous), year0(period of survey, 0,1 and 2), bcohdum(dummy of birth cohort, 0-7)

And I get sensible result from that.

But when I change the laplacian approximation into:

. xtmelogit overwt0 agetrc year0 bcohdum ||_all:R.year0||bcohdum:||pidlink: if s_analysis==1, intpoints(2)

I got the following error message after the second iteration: "Hessian has become unstable or asymmetric"

What does it mean and what shoudl I do next?

Any feedback would be very much appreciated.

Best regards,
Helda


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