THE IMPACT OF OUT-OF-STATE PRISON POPULATION ON STATE HOMICIDE RATES - DISPLACEMENT AND FREE-RIDER EFFECTS

Past studies of the impact of prison population on homicide rates have produced widely divergent results. Those using state-level data find small impacts, bzd those using national data find very large ones. We use displacement/free-rider theory to explore the difference between t hese results. Displacement, in the current context, refers to a crimin al's movement away from states with higher imprisonment rates. Free ri ding occurs when a state benefits from criminals being incarcerated in other states. If the displacement effect holds, a state's prison popu lation has a stronger impact on crime within the state than would be a ccomplished by deterrence and incapacitation alone. If the free-rider effect holds, higher prison populations outside the state reduce homic ide in the state because criminals are incapacitated elsewhere. Using vital statistics data for 1929 to 1992, we conduct separate homicide r egressions for each state using both in-state and out-of-state prison population as independent variables. We find that the out-of-state var iable has a much larger (negative) association with homicide, indicati ng substantial free riding. We also find evidence of a small displacem ent impact.