Measuring the Incapacitation Effect of Incarceration

犯罪学和犯罪经济学领域的一个中心问题是，监禁犯罪活动者能在多大程度上降低国家犯罪率。将监禁与犯罪联系起来的短期因果路径是双重的。首先，被监禁的人不能犯罪。第二，个人可能会因为受到监禁的威胁而却步。尽管这些想法很简单，但实证研究的结果差异很大。这项研究的大部分都面临一个关键问题：任何增加犯罪活动的社会力量都会增加监禁率。 例如，如果经济恶化，更多的人因此而犯罪，更多的人将被逮捕并送进监狱。总的来说，我们观察到犯罪随着监禁的增加而增加，造成了监禁增加犯罪的错误印象。本项目将利用一个不寻常的政策事件来衡量监禁对犯罪的影响。2006年8月，意大利政府释放了全国三分之一的囚犯，以缓解监狱过度拥挤的状况。任何刑期不足三年的囚犯都将立即获释。结果，2006年8月，意大利监狱人口突然、离散和大幅下降。由于监禁的这种变化显然是由政策选择而不是导致犯罪的外部因素的变化驱动的，因此，围绕赦免的任何可观察到的犯罪变化都可以归因于监狱人口的变化。该项目将评估这一赦免对意大利犯罪率的影响。由此产生的实证结果将提供释放囚犯造成的犯罪数量的估计数，并将用于产生通过监禁预防的年度犯罪的估计数。最重要的是，该项目提供的估计数将不存在犯罪对监禁的负面影响方面的偏见。

A central question in the fields of criminology and the economics of crime concerns the extent to which incarcerating the criminally active reduces national crime rates. The short-run causal pathways connecting incarceration to crime are two-fold. First, those who are incarcerated cannot commit crimes. Second, individuals may be deterred by the threat of incarceration. Despite the simplicity of these ideas, the results from empirical research vary considerably. Much of this research suffers from a key problem: any societal forces that increase criminal activity will increase the incarceration rate. For example, if the economy were to sour and more people commit crime as a result, more people will be arrested and sent to prison. In the aggregate, we observe crime increasing as incarceration increases, creating the false impressions that incarceration increases crime.This project will measure the effect of incarceration on crime by making use of an unusual policy event. In August 2006, the Italian government released one-third of the nation's prison inmates in an effort to relieve prison overcrowding. Any inmate with less than three years remaining was immediately released. As a result, in August of 2006 the Italian prison population declined abruptly, discretely, and substantially. Since this change in incarceration was clearly driven by a policy choice rather than changes in external factors that cause crime, any observable changes in crime surrounding the pardon can be attributed to the change in the prison population. This project will evaluate the impact of this pardon on Italian crime rates. The resulting empirical results will provide estimates of the amount of crime caused by prisoner releases and will be used to produce estimates of the annual crimes prevented through incarceration. Most importantly, the project will provide estimates that are free from bias associated with a reverse impact of crime on incarceration.