DC's phony crime closure rates

This is one way to increase the closure rate. Put solved cases from many years in the numerator and only this year's cases in the denominator. From the Washington Post:

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. . . .