The world of economics is a complicated and messy place. Yet modern economic analysis rests on an attempt to represent the world by means of simple mathematical models. To what extent is this possible? How can such a program cope with the fact that economic outcomes are often driven by factors...

Economists have traditionally taken two very different approaches to studying market structure. One looks to "industry characteristics" to explain why different industries develop in different ways; the other looks to the pattern of firm growth within a "typical" industry to describe the...