An analysis of a state panel of prison populations from 1977 to 2005 shows that the best predictors of prison populations are crime, sentencing policy, prison crowding, and state spending. Prison populations grew at roughly the same rate and during the same periods as spending on education, welfare, health and hospitals, highways, parks, and natural resources. Current and lagged values of state spending on prison construction also accounted for a substantial amount of variation in subsequent prison populations. Public opinion, partisan politics, the electoral cycle, and social threats seem to have had little effect on the number of prisoners.
The availability of publicly acceptable alternatives to incarceration may not be sufficient to reverse course. Federal funding of alternatives—but not prisons—would provide states with the financial incentive to reduce prison populations.