Understanding and quantifying the determinants of the number of sectors or firms exporting in a given country is of relevance for the assessment of trade policies. Estimation of models for the number of sectors, however, poses a challenge because the dependent variable has both a lower and upper...

Helpman, Melitz, and Rubinstein (2008)�HMR�present a rich theoretical model to study the determinants of bilateral trade flows across countries. The model is then empirically implemented through a two-stage estimation procedure. This note seeks to clarify some econometric aspects of the...

We extend the simulation results given in Santos Silva and Tenreyro (2006, �The log of gravity,� The Review of Economics and Statistics, 88, 641-658) by considering data generated as a finite mixture of gamma variates. Data generated in this way can naturally have a large proportion of zeros...

In this note we identify and illustrate some shortcomings of the poisson com- mand in STATA. Specifically, we point out that the command fails to check for the existence of the estimates and show that it is very sensitive to numerical problems. While these are serious problems that may prevent...