Simultaneity complicates the estimation of the causal effect of police on crime. We overcome this obstacle by focusing on a mass layoff of Oregon State Police in February of 2003. Due solely to budget cuts, 35 percent of the roadway troopers were laid off, which dramatically reduced citations. The subsequent decrease in enforcement is associated with a significant increase in injuries and fatalities. The effects are similar using control groups chosen either geographically or through data-driven methods. Our estimates suggest that a highway fatality can be prevented with $309,000 of expenditures on state police. (JEL H76, K42, R41)

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We conduct laboratory experiments to investigate the effects of deterrence mechanisms under controlled conditions. The effect of the expected cost of punishment of an individual's decision to engage in a proscribed activity and the effect of uncertainty on an individual's decision to commit a violation are very difficult to isolate in field data. We use a roadway speeding framing and find that (a) individuals respond considerably to increases in the expected cost of speeding, (b) uncertainty about the enforcement regime yields a significant reduction in violations committed, and (c) people are much more likely to speed when the punishment regime for which they voted is implemented. Our results have important implications for a behavioral theory of deterrence under uncertainty.Keywords Deterrence . Experiment . Uncertainty . Crime and punishment JEL classifications C91 . D03 . D81 . K42The use of deterrence mechanisms-such as the probability of apprehension, fines, jail sentence length, and legal liability-in preventing proscribed activities is theoretically well understood: increases in the expected cost of committing illegal activities will reduce the amount of crimes committed.

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