中文摘要
警察机构投入大量资源以尽量缩短到达犯罪现场所需的时间。尽管如此，长期以来的共识是，警察响应时间对抓获犯罪嫌疑人的可能性没有实质性影响。我们利用大曼彻斯特警察局一份独特且丰富的数据集重新审视了这一问题。为识别因果效应，我们采用了一种新颖的策略，即利用彼此相邻但分处辖区边界两侧的地点在到响应站点距离上的不连续性。与以往证据相反，我们发现了大且强统计显著的效应：在我们偏好的估计中，响应时间增加10%会使破案的可能性下降4.7个百分点。我们发现，盗窃案的效应强于暴力犯罪，尽管对每一类犯罪而言效应都很大。我们发现了支持两种机制的提示性证据：即时逮捕的可能性以及嫌疑人被受害人或证人指认的可能性，都会随响应时间变快而上升。我们认为，在保守假设下，多聘用一名响应警员所带来（以未来被预防的犯罪衡量）的收益，相当于其工资成本的170%。
Abstract
Police agencies devote vast resources to minimizing the time that it takes them to attend the scene of a crime. Despite this, the long-standing consensus is that police response time has no meaningful effect on the likelihood of catching offenders. We revisit this question using a uniquely rich dataset from the Greater Manchester Police. To identify causal effects, we use a novel strategy that exploits discontinuities in distance to the response station across locations next to each other, but on different sides of division boundaries. Contrary to previous evidence, we find large and strongly significant effects: in our preferred estimate, a 10% increase in response time leads to a 4.7 percentage points decrease in the likelihood of clearing the crime. We find stronger effects for thefts than for violent offences, although the effects are large for every type of crime. We find suggestive evidence in support of two mechanisms: the likelihood of an immediate arrest and the likelihood that a suspect will be named by a victim or witness both increase as response time becomes faster. We argue that, under conservative assumptions, hiring an additional response officer would generate a benefit, in terms of future crime prevented, equivalent to 170% of her payroll cost.