estimate that crime fell roughly 20% between 1997 and 2014 due to legalized abortion. The cumulative impact of legalized abortion on crime is roughly 45%, accounting for a very substantial portion of the roughly 50-55% overall decline from the peak of crime in the early 1990s." Levitt discusses this paper and the background and history of the original paper (including its criticisms) in an episode of the Freakonomics podcast. Prison population Levitt's 1996 paper on prison population uses prison overcrowding litigation to estimate that decreasing the prison population by one person is associated with an increase of fifteen Index I crimes per year (Index I crimes include homicide, forcible rape, robbery, aggravated assault, burglary, theft, motor vehicle theft, and arson). Police hiring In a 1997 paper on the effect of police hiring on crime rates, Levitt used the timing of mayoral and gubernatorial elections as an instrumental variable to identify a causal effect of police on crime. Past studies had been inconclusive because of the simultaneity inherent in police hiring (when crime increases, more police are hired to combat crime). The findings of this paper were found to be the result of a programming error. This was pointed out in a comment by Justin McCrary published in the American Economic Review in 2002. In a response published with McCrary's comment Levitt admits to the error and then goes on to offer alternative evidence to support his original conclusions. Levitt's 1997 paper was also criticized in another comment that demonstrates the weakness of the instrumental variables used in the original study, rendering the interpretation difficult if not impossible. LoJack Ayres and Levitt (1998) used a new dataset on the prevalence of LoJack automobile anti-theft devices to estimate the social externality associated with its use. They find that the marginal social benefit of Lojack is fifteen times greater than the marginal social cost in high crime areas, but that those who install LoJack obtain less than ten percent of the total social benefits. Criminal age Another 1998 paper finds that juvenile criminals are at least as responsive to criminal sanctions as adults. Sharp drops in crime at the age of maturity suggest that deterrence plays an important role in the decision to commit a crime. Finances of a drug gang Levitt and Sudhir Alladi Venkatesh (2000) analyzed a unique dataset which details the financial activities of a drug-selling street gang. They found