It depends a lot on the reporting rate for the kind of crime being monitored; things like drug use - where enforcement is almost entirely dependent on police ac

It depends a lot on the reporting rate for the kind of crime being monitored; things like drug use - where enforcement is almost entirely dependent on police action - will absolutely be subject to this kind of positive bias. On the other hand, violent crimes, like shootings, are events that are (usually) observed regardless of police involvement. There's been some pretty interesting work on this in Richmond, CA, up north of Berkeley: http://www.thisamericanlife.org/radio-archives/episode/555/the-incredible-rarity-of-changing-your-mind?act=2#play http://www.thisamericanlife.org/radio-archives/episode/555/t... Basically, it was noticed that a small cluster of people were involved in most of the violent crime, and started interventions to make that cluster less likely to engage in violent crime.