Per capita income in the richest countries of the world exceeds that in the poorest countries by more than a factor of 50. What explains these enormous differences? This paper returns to an old idea in development economics and proposes that complementarity and linkages are at the heart of the...

December 15, 1998 -- Version 1.0 <p> The property that ideas are nonrivalrous leads to a tight link between idea-based growth models and increasing returns to scale. In particular, changes in the size of an economy's population generally affect either the long-run growth rate or the long-run level...</p>