Jonathan Klick, professor of law and economics at Florida State University, had an idea for how to examine a difficult social science question: Do more police officers in fact reduce crime?

Over and over again, myopic economists answer this question by excluding important independent variables, like you are about to see.

In a paper titled “Using Terror Alert Levels to Estimate the Effect of Police on Crime” (a copy of the article is available here) Klick and Tabarrok argued that changes in the national terror alert (“green”, “yellow”, “orange”, “red”, etc.) corresponded to shifts in crime levels.

“On high-alert days,” they wrote, ”total crimes decrease by an average of seven crimes per day, or approximately 6.6 percent.”

And, every $1 to add officers would reduce the costs of crime by $4.

By measuring elasticities for auto theft and other street crimes while the terror alert is high as opposed to when it is low, the economists conclude with a straight face that “if we had a 10 percent increase in police, crime would go down by about 4 percent.” Nationally, ”that means about 700,000 fewer property crimes and 213,000 fewer violent crimes.”

Or in other words,an increased threat of terrorism makes America’s streets safer. Only the economists’ argument is for carefully designed to talk only about the ‘effect of police on crime’, not the ‘effect of expected terrorism on the person in the street’.

All surface-level discussion of urban social policies emerges from a context of fragmented thinking. Many theoretical accounts in political science, economics, criminal justice, are not validated, or held to rigorous social scientific (more broadly defined) standards. But this does not stop us from implementing flawed policies. Even if terror alerts or the number of police decrease crime on a superficial level like this, it is still highly contestable whether an emergency policed state is the social meaning of order and security.

Professor Klick offered an even more striking suggestion to a NYTimes reporter. ”It wouldn’t be unreasonable,” he said, ”based on our estimates and based on conservative estimates of the costs of crime, to say it would be cost-effective to actually double the number of people working in police forces, which is pretty amazing.”