Dear Gabriele Rovigatti ,

I am estimating a production function on COMPUSTAT data for the U.S. and using prodest:

prodest y, method(op) free(lcogs) proxy(i) state(k) poly(3) reps(50)

y = ln(revenue)
lcogs = ln(cost of goods sold)
i =ln(investment)
k = ln(cpaital)

How is it possible that the first time I obtain: Array





And now that I had to rerun it again because I close the do file for a moment, I get this:



. prodest y, method(op) free(lcogs) proxy(i) state(k) poly(3) reps(50)
.........10.........20.........30.........40...... ...50


op productivity estimator Cobb-Douglas PF

Dependent variable: revenue Number of obs = 199521
Group variable (id): id Number of groups = 19442
Time variable (t): year
Obs per group: min = 1
avg = 10.3
max = 61

------------------------------------------------------------------------------
year | Coef. Std. Err. z P>|z| [95% Conf. Interval]
-------------+----------------------------------------------------------------
lcogs | -1.131983 .0763131 -14.83 0.000 -1.281554 -.9824126
k | 1.125322 . . . . .
------------------------------------------------------------------------------
Wald test on Constant returns to scale: Chi2 = 174.01
p = (0.00)



Same data, number of observations, everything, I did not touch anything. Now, I have tried more times and keep getting the same or similar coefficient values, like -1.13 for the lcogs variable. Why was it able to give me correct results once but now every time I repeat it, those are pretty similar but very bad values. Appreciate the help. Thanks.