Dear all.

I am a completely new user of Stata.

I am currently working in a international trade research to Colombia.

I read many post in statalist to understand how can I run stata with PPML.

I read that xtpoisson and ppml should give us the same results but I have tried many times and the results are not the same.

These are the commands and results:

xtpoisson x log_gdp_o log_gdp_d log_distw

------------------------------------------------------------------------------
x | Coef. Std. Err. z P>|z| [95% Conf. Interval]
-------------+----------------------------------------------------------------
log_gdp_o | .4846562 .0003929 1233.53 0.000 .4838861 .4854262
log_gdp_d | .4180332 .0003394 1231.63 0.000 .417368 .4186985
log_distw | -.7425596 .0186989 -39.71 0.000 -.7792087 -.7059105
_cons | -11.35575 .1625527 -69.86 0.000 -11.67435 -11.03716
-------------+----------------------------------------------------------------
/lnalpha | 1.438664 .0090369 1.420952 1.456377
-------------+----------------------------------------------------------------
alpha | 4.215063 .0380912 4.141063 4.290385

ppml x log_gdp_o log_gdp_d log_distw

------------------------------------------------------------------------------
| Robust
x | Coef. Std. Err. z P>|z| [95% Conf. Interval]
-------------+----------------------------------------------------------------
log_gdp_o | .8283028 .0092983 89.08 0.000 .8100785 .8465271
log_gdp_d | .7096657 .009622 73.75 0.000 .6908069 .7285244
log_distw | -.761988 .0122063 -62.43 0.000 -.7859119 -.7380641
_cons | -27.64312 .3506973 -78.82 0.000 -28.33047 -26.95577
------------------------------------------------------------------------------

As I said before, I am new in Stata and my question could be very simple but I would be so grateful to receive your help.

Best wishes.