The mayoral campaign is a great occasion to get newcomers like myself acquainted with the big issues in this town. One of these, stop-and-frisk, the US equivalent to the UK’s stop-and-search policy, has been under attack as it disproportionately targets Blacks and Hispanics.

(See update below.) New Yorkers will vote for their new mayor on 5 November. Incumbent Michael Bloomberg’s third term is up and he cannot stand for reelection. With him, a 20-year era of Republican mayors will most likely come to an end. His predecessor, Republican Rudy Giuliani came to the office in 1993. And although Bloomberg left the GOP in 2007, he still ran on a Republican ticket in 2009.

These two mayors oversaw a drastic decline in New York’s crime rate. Just as an example, check the statistics in the precinct where I live and compare today with 1990. Staggering. The conservative political establishment would attribute a large chunk of this to the two mayors’ and their police staff’s hardline policies, dubbed “fixing broken windows” for their zero tolerance toward smaller crimes.

In truth it is exceedingly difficult to explain just why the city’s crime rate dropped so precipitously. Oft-quoted from the popular science reading stacks, Malcolm Gladwell (The Tipping Point) would agree with the crime-fighting argument whereas Steven Levitt (Freakonomics) thinks that the increasing availability of contraception in the 1970s decreased the amount of unwanted children (although that line of reasoning has largely been dismissed since).

Other factors that are often quoted are the economic boom in the 1990s that drastically reduced unemployment and increased minimum wages as well as growth in the number of police forces. The end of the crack-cocaine epidemic also helped. All things considered, increased policing and a tougher line on crime had a statistically significant effect though.

“Stop and frisk” as well as “stand your ground” are widely seen as two very important proponents of this. However, both have become the target of rights activists recently, and rightly so in my opinion.

Stop and frisk happens disproportionately often to Blacks and Hispanics. NYPD would argue that this is a just a reaction to cold crime statistics, where these two groups dominate the charts for both criminals and victims categories. Yet racial profiling seems to extend beyond that and appears to at least partly stem from an “unconscious bias”. Apparently, Blacks and Hispanics move “furtively” more often than Whites, statistics of the police show.

A  campaign to end the current practice of the policy reached an important milestone when Judge Scheindlin ruled it unconstitutional and required the NYPD to review and change its current handling of stop and frisk. Mayor Bloomberg has already warned that the low crime rates could be in danger of reversing. Philadelphia may be an interesting case study.

Stand-your-ground, the famously tough American self-defence law, is given by some as a another reason of falling crime rates. Yet it also leads to tragic cases like Trayvon Martin’s, a Black teenager, who got killed in Florida recently. Martin’s murderer was acquitted under an extremely lax interpretation of the law which again disproportionately affects Blacks.

Yet there is a also a vocal group of people who defend racial profiling and criticise the colour-blindness. They say that if it is proven that tougher policing reduces crime and that crime is more likely committed by Blacks, you should stop and frisk accordingly. They also remind people of the state of chaos New York had been in at the onset of the change in policing, perhaps conflating their argument somewhat.

Of course no one wants to go back to the chaos of the 1970s and 80s. But can you still afford to racially profile when the evidence is flimsy at the very least?

Update: In the comments Moritz posts a link to this intriguing Mother Jones article on the correlation between lead exposure and crime rates. Despite seemingly compelling evidence, this theory has not gained a lot of traction in criminologists’ circles. If proven, it would render many sociological explanations of crime unhelpful and ultimately ideological. Powerful stuff.