Dear reader,
I have some trouble with performing a Stochastic Frontier Analysis in Stata
vs8.0. I hope you can help me out, the following is the problem:
The generated output from my Stata set-up gives comparable but different
output then my Limdep set-up (with same input):
the coefficients only differ by small percentages, this need not be a
problem
Stata gives an extreme big t-value, which seems quiet akward
as Limdep gives inefficiency numbers between 0 and 1, but Stata gives
'u' and 'te' values with the same value as 'xb' and the fitted dependent
variable (lnTKhat) (with value around 14). Clearl;y this is not correct.
(Limdep: Inefficiency observation 1=.1651, Stata: te obs 1 = 14,0888)
Can you please let me know what the problem is for giving wrong 'u' and
'te' values?
see the following log
frontier lnTK lnZT, d(e) cost;
Stoc. frontier normal/exponential model Number of obs =
15
Wald chi2(1) =
1.115e+12
Log likelihood = 8.5130782 Prob > chi2 =
0.0000
------------------------------------------------------------------------------
lnTK | Coef. Std. Err. z P>|z| [95% Conf.
Interval]
-------------+----------------------------------------------------------------
lnZT | 1.244566 1.18e-06 . 0.000 1.244563
1.244568
_cons | -4.327623 .0000181 . 0.000 -4.327659
-4.327588
-------------+----------------------------------------------------------------
/lnsig2v | -39.73655 977.6138 -0.04 0.968 -1955.824
1876.351
/lnsig2u | -3.135077 .5163978 -6.07 0.000 -4.147198
-2.122956
-------------+----------------------------------------------------------------
sigma_v | 2.35e-09 1.15e-06 0
.
sigma_u | .2085579 .0538494 .1257324
.3459441
sigma2 | .0434964 .0224614 -.0005272
.08752
lambda | 8.87e+07 .0538494 8.87e+07
8.87e+07
------------------------------------------------------------------------------
Likelihood-ratio test of sigma_u=0: chibar2(01) = 7.84 Prob>=chibar2 =
0.003
. predict lnTKhat;
(option xb assumed; fitted values)
. predict xb;
(option xb assumed; fitted values)
. predict u;
(option xb assumed; fitted values)
. predict te;
(option xb assumed; fitted values)
. list lnTK lnTKhat xb u te;
+------------------------------------------------------+
| lnTK lnTKhat xb u te |
|------------------------------------------------------|
1. | 14.16382 14.00888 14.00888 14.00888 14.00888 |
2. | 14.32893 14.30058 14.30058 14.30058 14.30058 |
3. | 16.78383 16.78383 16.78383 16.78383 16.78383 |
4. | 13.81136 13.81136 13.81136 13.81136 13.81136 |
5. | 13.54609 13.30281 13.30281 13.30281 13.30281 |
etc
Thanks and regards,
Erik Brouwer
[email protected]
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