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st: System of Seemingly Unrelated Poisson Regressions (with Constraints)

From   "Markus Lampe" <>
Subject   st: System of Seemingly Unrelated Poisson Regressions (with Constraints)
Date   Sat, 7 Jun 2008 10:48:37 +0200

Dear Subscribers,

I am working with bilateral trade gravity models on a disaggregated
level to find out if bilateral trade treaties which preferentially
lowered tariffs on specific commodities enhanced respective trade
flows. I used to do that with a quite simple system of log-linear
sureg regressions like

ln(bilateralimportcommodity1)=a1 + b1 ln(incomeimporter)+c1
ln(distance)+d1 tariff-preference-dummy [and lots of control
ln(bilateralimportcommodity2)=a + b2 ln(incomeimporter) + c2
ln(distance) + d2 tariff-preference-dummy [and lots of control
for several goods

to estimate an "overall average effect" I restricted d1=d2=d3, etc.

Now I got aware of a newer literature on gravity models that bothers
about biases caused by "0" observations in the import matrix that are
excluded by taking the logs. Santos Silva and Tenreyro, The Log of
Gravity, Review of Economics and Statistics 88, 2006, 88(4), 641-658.

I now that I might estimate poisson regressions in dependent variable
levels and later use surest, but this does not allow me to impose

Does anyone have any idea about the feasibility of my idea (a system
of SU poisson regressions with constraints) or has ever tried
something alike?

I had a look at Gary  King's, A Seemingly Unrelated Poisson Regression
Model, in Sociological Methods and Research 17/3, 1989, 235-255, but
found no implementations, etc.

Thank you very much for your consideration


Markus Lampe
Institute for Economic and Social History
University of Muenster
Domplatz 20-22
D-48143 Muenster (Germany)
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