Heterogeneity and Aggregation

摘要

Macroeconomics is one of the most important fields of economics. It has perhaps the grandest goal of all economic study, which is to advise policymakers who are trying to improve the economic well-being of entire populations of people. In the mid-twentieth century, say from 1940 to 1970, macroeconomics had an orientation toward its role much like an oracle giving advice while peering down from the top of a mountain. That is, while economists could see people making detailed decisions about buying products, investing their wealth, choosing jobs or career paths, etc., macroeconomic models were extremely simple. For instance, describing the aggregate consumption of an entire economy could be done with taking into account just a few variables: aggregate income, lagged aggregate consumption, etc. Such equations often fit aggregate data extremely well. Unfortunately, such models could not predict future aggregate variables with sufficient precision to dictate optimal policies. Even with great statistical fit, there was too much uncertainty as to what the underlying processes were that drove the aggregate data, and for policy prescriptions, it is crucial to know something about those processes.