How useful are NYC's crime numbers?

From the New York Times "NYPD Leaves Offenses Unrecorded to Keep Crime Numbers Down" (Al Baker and Joseph Goldstein, December 30, 2011):

Crime victims in New York sometimes struggle to persuade the police to write down what happened on an official report. The reasons are varied. Police officers are often busy, and few relish paperwork. But in interviews, more than half a dozen police officers, detectives and commanders also cited departmental pressure to keep crime statistics low.

While it is difficult to say how often crime complaints are not officially recorded, the Police Department is conscious of the potential problem, trying to ferret out unreported crimes through audits of emergency calls and of any resulting paperwork.

As concerns grew about the integrity of the data, the police commissioner, Raymond W. Kelly, appointed a panel of former federal prosecutors in January to study the crime-reporting system. The move was unusual for Mr. Kelly, who is normally reluctant to invite outside scrutiny.

The panel, which has not yet released its findings, was expected to focus on the downgrading of crimes, in which officers improperly classify felonies as misdemeanors.

But of nearly as much concern to people in law enforcement are crimes that officers simply failed to record, which one high-ranking police commander in Manhattan suggested was “the newest evolution in this numbers game.” . . .

The article then contains a long list of examples where crimes weren't recorded by the police. This next point is something that every economist would understand;

Despite the new guidelines, some critics say subtle tweaks in police protocol offer opportunities to avoid taking reports. In 2009, the department came up with a new policy that might seem inconsequential: Robbery victims would have to go to the station house to give their reports directly to a detective or patrol supervisor.

The intent was to get an investigator on the case as quickly as possible, but one police commander said supervisors were aware that another consequence could be that fewer crimes would be reported.

The policy was restored to its original form last year, with uniformed officers once again allowed to take the initial report of a robbery. “A police report wouldn’t get made because they make you wait in the police station for hours,” one commander said. Eventually, he added, the crime victim would give up and leave.