Incarceration and the Law of Diminishing Marginal Returns

A substantial body of research shows that a small group of repeat offenders accounts for a disproportionate share of criminal activity and that many high-rate offenders are already incarcerated. This pattern underlies the law of diminishing marginal returns, which predicts that continued expansion of incarceration should increasingly sweep in less dangerous offenders and yield declining public safety benefits. Using 2009 State Court Processing Statistics linked to county-level incarceration rates, we employ multilevel models to examine whether offense seriousness and prior criminal history exert weaker effects in higher-incarceration counties. Contrary to this expectation, both factors remain strong and stable predictors across counties, including those with very high incarceration rates. The composition of the incarcerated population does not shift toward less dangerous offenders as incarceration increases. These findings help explain why continued incarceration growth yields limited public safety gains and suggest that decarceration can be pursued with minimal risk to community safety.