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st: opreg and levpet not working

From   Jerry Slice <>
Subject   st: opreg and levpet not working
Date   Mon, 28 Feb 2011 22:55:01 -0500

I'm trying to estimate a production function using opreg to control for selection, and levpet without the selection control. Using Stata 11.1, I get the following error on both of them:

(levpet) no observations
error #2000 occurred in program nllp_bs_gmm

(opreg) no observations
an error occurred when bootstrap executed opreg

The commands I am using are:
opreg sales, exit(exit) state(cap) proxy(inv) free(emp)
levpet sales, free(emp) proxy(inv) capital(cap) revenue

I have no missing data values, so I don't understand what the issue is here. There are no mis-casts as strings, and everything is properly formatted. Does anyone know how to fix this issue?

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