Estimating the extensive margin of trade
研究如何准确估计一国出口部门或企业数量（扩展边际）的决定因素，提出一种考虑因变量上下界的新估计方法，避免传统方法因忽略边界导致的偏误。
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 bound, implying that the partial effects \nof the explanatory variables on the conditional mean of the dependent variable cannot be constant and must approach zero as the dependent variable approaches the bounds. \nWe argue that ignoring these bounds by using OLS or count-data models that ignore the upper bound can lead to erroneous conclusions due to the model's misspecification. \nWe propose a flexible specification that accounts for the doubly-bounded nature of the dependent variable. We empirically investigate the problem and the proposed solution, and find significant differences between estimates obtained with the proposed estimator and those obtained with standard approaches.