This paper provides evidence on the monopolistic competition model with heterogeneous firms and endogenous productivity. We show that this model has a well-defined GDP function where relative export variety enters positively, and estimate this function over 48 countries from 1980 to 2000....

The elasticity of substitution between goods from different countries—the Armington elasticity—is important for many questions in international economics, but its magnitude is subject to debate: the "macro" elasticity between home and import goods is often found to be smaller than the...