So why are so many so enamored of these dubious tactics?

Stop-and-frisk proponents, like former New York City Mayor Michael Bloomberg, former NYPD Commissioner Raymond Kelly, and the criminologist Alan Zimring believe that the method is effective because of what they have seen in New York. Crime dropped precipitously in the 1990s, they say, and the reason for it is the distinctive way the NYPD practiced policing.

This is an argument that—in both style and substance—runs counter to modern methods of empirical research. The NYPD did not implement large-scale trials to isolate the effects of stop-and-frisk. nor did they look to any form of multivariate analysis examining the largest cities in the country. The argument is entirely based on people eyeballing statistics and telling stories.

So what about those stories? The simple version is that the NYPD adopted order-maintenance policing, including stop-and-frisk, and crime went down. But the increase in frisks and arrests didn’t predate the drop in crime; it came after the drop in crime. If we widen our perspective, we see that the crime drop in New York City, particularly for property offense, began long before 1990.

What about homicide? After all, citing that link was the most effective claim Bloomberg and Kelly used in support of stop-and-frisk. Well, here’s a piece of data you won’t hear any of the proponents tout: if you look at the 25 largest cities in the United States, only five had significantly higher homicide rates in 2010 than in 1960. Big cities—including New York City—are pretty much back where they started before the massive late-20th century crime-wave. Some of these cities did not see the stunning improvements in homicide rates that New York experienced in the 1990s, but that’s because they didn’t see dramatic increases in homicide rates in the preceding decades.

In cities where homicide rates did increase between 1960 and 1990, many display similar patterns to New York City. LA, Houston, San Antonio, San Diego, Dallas, Jacksonville, and Charlotte saw homicide rates move nearly parallel to New York City’s, although they started from, and returned to, different prior levels. Other cities, however, have homicide rates that are even lower than they were in 1960. And still others started with higher rates and ended with lower ones. You only get the pattern proponents describe by looking arbitrarily at particular cities and decades.

When you look at all the data and all the research, the puzzle is not so much why crime dropped in New York City, but what caused the great American crime wave in the first place. There are plenty of prominent theories. I’ll mention just two.

Lead. One possible factor is the widespread distribution of lead through motor vehicle exhaust, paint, and lead pipes —a distribution that was disproportionately concentrated in low-income inner-city neighborhoods. Children in New York have long been at particular risk compared with the rest of the country. The majority of the city's housing units were built before 1960, when the city phased out residential lead paint, and low-income families are the most likely to live in homes where the paint is deteriorating. Over the past two decades, health officials have made concerted efforts to address this problem. But the well-reported fact that inner-city families were exposed, and that two generations of low-income urban American suffered impaired cognitive development as a result, is tragic beyond measure. The close correlation between lead levels and crime rates—not just in New York, but in countries around the world—is brutal in its scope and implications.