An Institutionalization Effect: The Impact of Mental Hospitalization and Imprisonment on Homicide in the United States, 1934-2001

Bernard E. Harcourt, Columbia Law School


Previous research overwhelmingly shows that incarceration led to lower rates of violent crime during the 1990s, but finds no evidence of an effect prior to 1991. This raises what Steven Levitt calls “a real puzzle.” This study offers the solution to that puzzle: the fatal error with prior research is that it used exclusively rates of imprisonment, rather than a measure that combines institutionalization in both prisons and mental hospitals. Using state-level panel data regressions over the period 1934-2001, and controlling for demographic, economic, and criminal justice variables, this study finds a large, robust, and statistically significant relationship between aggregated institutionalization and homicide rates, providing strong evidence of what should now be called an institutionalization effect (rather than merely an incapacitation effect).