Why the Police Have an Effect on Violent Crime After All: Evidence from the British Crime Survey
研究发现，使用警方统计的犯罪数据会严重偏差威慑效应的实证检验。通过对比警方记录和受害者报告的犯罪数据，发现警察数量增加不仅降低犯罪率，还提高了暴力犯罪被警方记录的比例，导致估计偏差。
We present evidence that the use of police statistics as a source of crime data can seriously bias empirical tests of the model of deterrence. We use data for 21 areas in England and Wales in 2001–8. In addition to police-recorded crime data, we use victim-reported crime data from the British Crime Survey that are unaffected by changes in public reporting of crime and police recording of crime. We find that the estimated effect of the number of police on recorded and victim-reported crime is similar for property crime but different for violent crime. Our findings suggest that higher numbers of police not only reduce crime rates but also increase the share of crime, and in particular violent crime, that finds its way into police statistics. The resulting estimation bias is found to be large.