Geography, productivity, and trade: Does selection explain why some locations are more productive than others?
理论证明，在考虑异质性贸易成本和集聚与选择的不同空间尺度后，选择效应会影响地区生产率差异；实证发现集聚效应仍占主导，但选择效应的重要性显著上升。
Abstract Two main hypotheses are usually put forward to explain the productivity advantages of larger cities: agglomeration economies and firm selection. Combes et al. (2012) propose an empirical approach to disentangle these two effects and find no impact of selection on local productivity differences. We theoretically show that selection effects do emerge when heterogeneous trade costs and the different spatial scale at which agglomeration and selection may work are properly taken into account. Our empirical findings confirm that agglomeration effects play a major role. However, they also show a substantial increase in the importance of the selection effect.