The trick to D.C. police force’s 94% closure rate for 2011 homicides

Editor’s note

The article about the D.C. police department’s ­homicide-closure statistics suggested that the department may have manipulated data to foster a positive impression of the force’s performance.

Graphic

A tale of two rates.

Gallery

 Cathy Lanier has broken the mold for a big-city police chief. But has her department fudged its homicide data to achieve a 94 percent closure rate for 2011? Lanier says including homicide cases from other years that were closed last year is routine practice. Some law enforcement veterans say it’s not.

The article characterized the department’s reporting of homicide-closure rates as a “statistical mishmash that makes things seem much better than they are.” It also suggested that the department’s methodology produced a number that was not “a true closure rate.” As a result, the article, as well as elements of the headline and an accompanying graphic, implied that the department artificially inflated public data on the number of cases that are closed each year.

In fact, as the article reported, the department has followed practices consistent with federal crime-data guidelines and relied upon the same methodology used by other major municipal police agencies. The department hasn’t altered the ways it calculates homicide-closure rates since Cathy L. Lanier became chief in 2007, and it discloses its methodology in its annual report.

The data the department publicly reports include prior-year cases that are opened or closed during the calendar year. In recent years, the closures of cases from earlier years have tended to enhance closure rates. For capturing the department’s performance over time, that may be a statistically valid approach, although it could leave the impression that police are solving current-year cases faster than they actually are. The decision to publicly cite the higher rate casts the department in a more favorable light but does not mean that the underlying data are distorted.

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By Cheryl W. Thompson

For the past two months, D.C. Police Chief Cathy L. Lanier has touted the city’s astronomically high homicide closure rate — 94 percent for 2011 — and warned anyone contemplating murder in the District to think twice.

“Your risk of being caught is pretty high if you commit a homicide in D.C.,” Lanier told The Washington Post in December.

The closure rate she presents for the District is 154 percent higher than Boston’s and at least 104 percent higher than Baltimore’s, and it gives residents reason to believe that D.C. police have been remarkably successful at solving homicide cases under her watch.

But an examination of District homicides found that the department’s closure rate is a statistical mishmash that makes things seem much better than they are. The District had 108 homicides last year, police records show. A 94 percent closure rate would mean that detectives solved 102 of them. But only 62 were solved as of year’s end, for a true closure rate of 57 percent, according to records reviewed by The Post.

D.C. police achieved the high closure rate last year by including about 40 cases from other years that were closed in 2011.

Also: The mysterious closure rate of an award-winning D.C. detective

The cases date from 1989, records show. The pattern was first reported by a local Web site, homicidewatch.org, in D ecember.

Lanier said the department followed FBI Uniform Crime Reporting guidelines in calculating its homicide clearance rate.