"The Spelman and Brown report had important implications for the allocation of police resources: putting more money into speeding up police response times to 911 would be too expensive and would offer insufficient benefit to justify the expense. As Spelman and Brown found, "arrests that could be attributed to fast police response were made in only 2.9 percent of reported serious crimes."In short, gun-free zones like Washington D.C. and the People's Republic of Chicago apparently put their citizens at risk by not allowing them access to an "immediate response system" when attacked.
The real point of the article is that there are no statistics in recent Justice Department reports about "interrupted crime," that is, crimes that were interrupted or halted by the arrival of the gendarmes, summoned by a 911 call:
"When potential crime victims (i.e., everyone) consider whether to adopt particular defensive measures (locks, guns, window bars, alarms, etc.), they must make trade-offs of costs and benefits. For example, window bars might prevent a criminal from coming in, but they can also block the exit in case of a fire. For citizens to make well-informed decisions about self-defense, citizens ought to know how likely it is that the government will rescue them in an emergency.
"We cannot expect perfection from the police; after all, they travel by automobile or by foot, not by teleportation. We can expect that government or university researchers (many of whom are heavily subsidized by the federal government) would gather statistics directly relevant to life-or-death decisions."