The Growth of Prisons: Toward a Second Generation Approach

Over the past three decades, the US prison population has soared from 300,000 inmates to 1.5 million. In recent years, many scholars have devised rigorous empirical models to try to determine what forces have been most responsible for this impressive growth. This article reviews these studies and finds that all suffer from important shortcomings that limit the extent to which they accurately identify causal mechanisms. The problems are both technical and conceptual. Technically, most studies either fail to control for several significant empirical defects - such as endogeneity, omitted variable bias, and colinearity - or so do unconvincingly. Conceptually there are several issues. In some instances, for example, it is unclear whether the variable chosen to test a particular causal theory is an effective or accurate proxy; in others, the theory itself does not appear to be formulated correctly. This article sets forth the problems with the current studies and suggests technical and conceptual improvements for future work.