A cross country empirical investigation of the aggregate production function specification

Many growth models assume that aggregate output is generated by a Cobb-Doug las production function. In this article we question the empirical relevanc e of this specification. We use a panel of 82 countries over a 28-year peri od to estimate a general constant-elasticity-of-substitution (CES) producti on function specification. We find that for the entire sample of countries we can reject the Cobb-Douglas specification. When we divide our sample of countries up into several subsamples, we find that physical capital and hum an capital adjusted labor are more substitutable in the richest group of co untries and are less substitutable in the poorest group of countries than w ould be implied by a Cobb-Douglas specification.