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Wednesday, January 26, 2011

Checking the Stats: How to Verify NYPD Data

Franklin Zimring, a law professor from the University of California at Berkeley, says when it comes to recording crime statistics police departments are a little like an umpire officiating a game he has a bet on.

“That makes people deeply suspicious, and they should be,” said Zimring.

Critics of the New York Police Department’s crime statistics want to revive the sort of audit done in 1997 by former state Comptroller Carl McCall, as The Journal reported. Those pushing for new review point to allegations from a Brooklyn police officer named Adrian Schoolcraft, who went public last year with secretly taped recording that showed that some police supervisors in his Bedford-Stuyvesant precinct may have been downgrading crime complaints or refusing to take them at all.

What’s needed to check the police’s scorekeeping, he said, is independent corroboration. Zimring’s research focused on homicide, robbery and auto theft as reported by the NYPD from 1990 to 2009. He then compared these numbers to independent sources to verify or discount the sizable decline in each crime.

For example, Zimring said there was a 94% decline in stolen cars between 1990 and 2009, according to the NYPD statistics — the largest drop of any of the index crimes. His research showed that two databases for multiple insurance companies had about a 90% drop in stolen vehicle claims in the city over that period.

The professor says he was able to confirm the accuracy in the drop in robberies reported by the NYPD by comparing it to the department’s own statistics on the number of homicides in which robbery was the motive. He said the drop in robberies and robbery-homicides paralleled each other extremely closely. If anything, his data suggested that robberies during the early 1990s, which peaked at more than 100,000 one year and were 5 ½ times higher than today’s levels, might have actually been slightly under-reported.

Zimring, who is writing a book called “The City That Became Safe: New York and the Future of Crime Control,” states that changes in policing policies “are the only obvious candidates to take credit” for what he called the “Guinness Book of World Records’ crime drop” that occurred in the city from 1990 to 2009.

During that time, the city added 9,000 more cops in 1990, created a management philosophy focused on statistical measures known as CompStat and adopted more aggressive street policing tactics. Some of those policies, particularly police stopping hundreds of thousands of people a year in what are known as “stop and frisks,” have been controversial.

Comparing the crime declines in New York City to those in other big cities , Zimring found that the NYPD had a significant impact in decreasing the “three classic street crimes:” robbery, burglary and auto theft.

“Burglars have to use the streets to get to your apartment,” he said. “The robber meets you there and the auto thief steals your car off the street. So those are the street crimes, and there the contribution of police presence on the street is overwhelming.”

The impact the NYPD had on homicide and rape were less pronounced, and Zimring’s work showed that the city’s cops had a very limited role in lowering grand larcenies and assaults.

Zimring said his research found that over the past 20 years, New York City’s crime rate reduction is twice the national average and has lasted twice as long. And what is especially impressive about that crime drop is that since 1990 the number of people police locked up from New York City has declined by 28% while nationally the incarceration figure has gone up 65%.

“They haven’t been stuffing the prisons full in New York City,” he said. “Not only has New York done what everybody thought was impossible but New York has been playing by a very different set of rules from the rest of the country.”

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