Large cities produce more output per capita than small cities. This higher productivity may occur because more talented individuals sort into large cities, because large cities select more productive entrepreneurs and firms, or because of agglomeration economies. We develop a model of systems of cities that combines all three elements and suggests interesting complementarities between them. The model can replicate stylized facts about sorting, agglomeration, and selection in cities. It also generates Zipf 's law for cities under empirically plausible parameter values. Finally, it provides a useful framework within which to reinterpret extant empirical evidence. Abstract Large cities produce more output per capita than small cities. This may occur because more talented individuals sort into large cities, because large cities select more productive entrepreneurs and firms, or because of agglomeration economies. We develop a model of systems of cities that combines all three elements and suggests interesting complementarities between them. The model can replicate stylised facts about sorting, agglomeration, and selection in cities. It also generates Zipf's law for cities under empirically plausible parameter values. Finally, it provides a useful framework within which to reinterpret extant empirical evidence.

Abstract-We investigate the 2008-2009 trade collapse using microdata from a small open economy, Belgium. Belgian exports and imports mostly fell because of smaller quantities sold and unit prices charged rather than fewer firms, trading partners, and products being involved in trade. Our difference-in-difference results point to a fall in the demand for tradables as the main driver of the collapse. Finance and involvement in global value chains played a minor role. Firm-level exports-to-turnover and imports-tointermediates ratios reveal a comparable collapse of domestic and crossborder operations. Overall, our results reject a crisis of cross-border trade per se.

No abstract

SUMMARY We derive a quantity‐based structural gravity equation system in which both trade flows and error terms are cross‐sectionally correlated. This system can be estimated using techniques borrowed from the spatial econometrics literature. To illustrate our methodology, we apply it to a well‐known Canada–US trade dataset. We find that border effects between the USA and Canada are smaller than suggested by previous studies: about 7.5 for Canadian provinces and about 1.3 for US states. Hence controlling directly for cross‐sectional interdependence among both trade flows and error terms reduces measured border effects by capturing ‘multilateral resistance’. Copyright © 2010 John Wiley & Sons, Ltd.