We study the shape of the aggregate production function in the presence of land-intensive agriculture. The traditional Cobb-Douglas formulation is corrected to include a "diversification component." The implied TFP differences across countries are larger than what Solow residuals suggest.

Using a class of endogenous growth models that exhibit international spillovers, we show that most of the cross-country differences in output per worker are explained by barriers to the accumulation of rival factors (physical and human capital) rather than by barriers to the accumulation of...