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st: sureg

From   Mekbib Haile <>
To   "" <>
Subject   st: sureg
Date   Fri, 24 Aug 2012 04:30:41 -0700 (PDT)

Dear all,

I have 2 questions:

1.   After a sureg command on STATA using price levels, I wanted to estimate elasticities with the margins* command.

I have one problem with one of my equations: stata gives me the following error message.

. margins, eyex (l2.y  l.y  x1  x2  x3) predict(equation(y))
 could not calculate numerical derivatives -- discontinuous region with missing values encountered r(459);

However, my data has no missing values except for the lag variables. What could be a potential problem? The same command works fine when all the covariates were in logarthmic format.  

Do you also suggest estimating elasticities at mean (atmeans option) values or better to use the average of the elasticities of individual observations?

2.   How do I test and control for Heteroscedasticity after a Seemingly Unrelated Regression using STATA?

Many thanks!


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