Incarceration, committment and homicide rates
Two recent papers by Prof. Harcourt finds an inverse relationship between homicide and total incarceration rate (i.e., in prison and in mental institutions).
"First, at the national level, using the new, expanded data on mental institutions (including all institutions for those deemed mentally ill), the contrast between the midcentury and 2001 is even more pronounced: during the 1940s and 50s, the United States consistently institutionalized in mental hospitals and prisons at rates above 700 persons per 100,000 adults, reaching peaks of 778 in 1939 and 786 in 1955. The relationship between the expanded aggregated institutionalization and homicide rates over the period 1934 to 2000 is statistically significant at the national level, holding constant three leading correlates of homicide.
Second, the very same relationship exists at the state level. Using state-level panel data regressions spanning the entire period from 1934 to 2001, including all 50 states, and controlling for economic, demographic, and criminal justice variables, I find a large, robust, and statistically significant relationship between aggregated institutionalization and homicide rates. The predicted relationship is not linear, but involves some slight elasticity. The findings are not sensitive to weighting by population and hold under a number of permutations, including when I aggregate jail populations as well. "