Establishing a robust causal relationship between trade and income has been difficult. Frankel and Romer (1999) use a … geographic instrument to identify a positive effect of trade on income. Rodriguez and Rodrik (2000) show that these results are … the quantity of world trade carried by air to increase over time. Country pairs with relatively short air routes compared …

Establishing a robust causal relationship between trade and income has been difficult. Frankel and Romer (1999) use … variable problem by generating time varying geographic instruments. The quantity of world trade carried by air has been … aggregated and used as instruments for trade in a regression of income on trade. The time series variation allows for controls …