The Incidence of Gravity

The high trade costs inferred from gravity are rarely used in the wide class of trade models. Two related problems explain this omission of a key explanatory variable. First, national seller and buyer responses to trade costs depend on their incidence rather than on the full cost. Second, the high dimensionality of bilateral trade costs requires aggregation for most practical uses in interpretation or standard trade modeling. This paper provides an intuitive description of a resolution to the aggregation and incidence problems. For each product, it is as if each province or country sells to a world market containing all buyers and buys from from that market containing all sellers, the incidence of aggregated bilateral trade costs being divided between sellers and buyers according to their location. Measures of incidence described here give intuitive insight into the consequences of geography, illustrated with results from Anderson and Yotov (2008). The integration of the incidence measures with standard general equilibrium structure opens the way to richer applied general equilibrium models and better empirical work on the origins of comparative advantage.