Helpman, Melitz, and Rubinstein (2008)HMRpresent 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 estimation...

Helpman, Melitz, and Rubinstein (2008)HMRpresent 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 estimation...

Although economists have long been aware of Jensen's inequality, many econometric applications have neglected an important implication of it: estimating economic relationships in logarithms can lead to significant biases in the presence of heteroskedasticity. This paper explains why this problem...