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The facts about stop-and-frisk in New York City

Republican presidential nominee Donald Trump says he favors "stop-and-frisk." Here's what that means and why the policy is so controversial. (Video: Victoria Walker/The Washington Post)

Update: During the first presidential debate, Donald Trump again argued that stop-and-frisk was an effective deterrent in New York, and that the policy hadn't been ruled unconstitutional. It wasn't effective, and it was ruled unconstitutional. Updates below.

Rudy Giuliani's political reputation hinges a great deal on the drop in crime that occurred while he was mayor of New York City. He used that fact to great effect during his energetic speech at the Republican convention, arguing for Donald Trump's candidacy by saying that he knew Trump would fight crime just as effectively as he had himself. "What I did for New York, Donald Trump will do for America," Giuliani argued.

In an interview with Fox News's Sean Hannity that airs Wednesday night, Trump will pledge to do exactly that. According to a transcript, Trump tells the talk show host -- an overt Trump supporter -- that he will introduce the policy of stop-and-frisk that began in the New York police department during Giuliani's time in the mayor's office.

Under stop-and-frisk, New York police officers were empowered to detain and search people for often-vague pretexts. (A Twitter account tweeted thousands of examples of the reasons for such stops.) If any illegal item or substance was found, an arrest resulted.

"We did it in New York," Trump tells a member of the audience, adding that "it worked incredibly well and you have to be proactive and, you know, you really help people sort of change their mind."

Here's what Trump said the next day, according to a transcript from CBS' Sopan Deb.

Rudy Giuliani did a great job as mayor and they really straightened things out with stop-and-frisk, and it was used further by the next mayor, Bloomberg, and now they, you know, recently -- not so recently but fairly recently -- they stopped it. But stop-and-frisk worked. We had tremendous shootings, number of shootings. Now Chicago is out of control. And I was really referring to Chicago with stop-and-frisk. ... I was talking about stop-and-frisk for Chicago.

But it didn't work really well -- or, at least, there's no real correlation between the use of stop-and-frisk and New York's reduction in crime.

The New York Civil Liberties Union has collected data on stop-and-frisks from 2002 to the present. We can compare that to FBI data on crime rates (including preliminary 2015 estimates from the Brennan Center for Justice) and see how the use of the tactic compared to the rate of violent crimes or murders.

Simply put, there's almost no correlation.

(Notice, too, that Giuliani's claim that he deserves credit for New York's crime rate is also overblown. The plunge began before he took office, in parallel with a sharp national drop in crime levels. It continued after he left.)

Crime in New York declined quickly after 1990 and has generally stayed low. There was a brief uptick last year at the same time as a further drop in the stop-and-frisk count, but in four of the past five years, levels of crime fell alongside the number of stop-and-frisks. Supporters of the policy often point specifically to gun crimes as a rationale for its use (since the policy often aimed at finding illegal firearms on suspects), but 2016 saw the fewest shootings during the first six months of the year in decades.

A separate study looked at whether or not the policy had a significant effect on the number of robberies and buglaries in New York. No effect was found.

The broader problem with stop-and-frisk was that it was applied heavily to communities of color. More than half of those detained and searched, according to the NYCLU's data, were black, and nearly a third were Latino.

That's part of the reason that the NYCLU has the data: A federal judge determined that the NYPD needed to release data on its application of stop-and-frisk on a quarterly basis as part of a settlement of a lawsuit filed in 1999 charging that black New Yorkers were unfairly targeted. That claim was bolstered when a New York police officer recorded conversations with his superior officers in which they told him to target black and Hispanic people.

Michael Bloomberg, who followed Giuliani as mayor, often argued that nonwhites weren't targeted enough. "I think we disproportionately stop whites too much and minorities too little. It’s exactly the reverse of what they say," he said in a radio interview in 2013. His argument was that crime was more of a problem with young nonwhite men. This was during a mayoral election year, and Bill De Blasio made shutting down stop-and-frisk a key part of his campaign. He won.

After Republican presidential candidate Donald Trump lamented the end of “stop and frisk” in New York, debate moderator Lester Holt stepped in. (Video: The Washington Post)

In every year, at least 80 percent and often 90 percent of those who were stopped were found not to have done anything wrong. When he was the city's public advocate, before being elected mayor, De Blasio released a report on the practice, finding that stops of whites were twice as likely to result in discovery of a weapon as a stop of a black person and that blacks were only two-thirds as likely as whites to be carrying something illegal. In other words: Most people were innocent, but whites who were stopped were more likely to be breaking laws regarding weapons or contraband.

In 2013, a federal judge determined that the policy of stop-and-frisk in New York City was discriminatory and unconstitutional. The city challenged the ruling, but the transition to the new mayor in 2014 meant that the appeal was dropped. The practice is still viewed very negatively by communities of color in New York City.

On Monday, new data from the Brennan Center revealed that the recent increase in crime is modest and that the increased murder rate in Chicago will likely be responsible for half of the national increase in 2016. Chicago's problem is serious and severe and needs to be addressed. History doesn't suggest that stop-and-frisk is an effective way to address it -- and it suggests that Rudy Giuliani may not have as many answers as he thinks.