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st: frontier - ufrom- specify matrix


From   "Georgeta Vidican" <gvidican@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: frontier - ufrom- specify matrix
Date   Fri, 16 Feb 2007 11:23:51 -0500

Dear all,

I would appreciate some help on the following issue, as I am new to
stata and frontier analysis.

I am fitting a truncated normal stochastic frontier model (6 inputs
-I, and 3 covariates -C) but I run into the problem of not being able
to run de model with using the "ufrom" option. I'll write the steps I
went through so that you get an idea of where I stumble:

- I first run the model "frontier O I1...I6, d(tnormal) cm(C1..C3)

- since I get the message "initial values not specified", I try to get
the starting values for the ML estimator by running an OLS regression
on O I1...I6, getting the matric by "matrix b0=e(b), ln(e(rmse)^2),
.1"  (QUESTION: should I run the regression including the covariates
as well?)

- I re-run the model as "frontier O I1...I6, d(tnormal) ufrom(b0) cm(C1...C3)"

However, I get the message that "ufrom() must specify a 1x12 matrix"

I would really appreciate your suggestions on how to fix this problem.
It is most probably an easy procedure.

Many thanks.
Georgeta
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