Sexual assaults across the District spiked nearly 50 percent in the first five months of 2010 over the same period last year, according to internal police documents obtained by The Washington Examiner.

From Jan. 1 to June 8 there were 82 sexual assaults in the city, up from 56 during the same period in 2009, the documents show.

But Chief Cathy Lanier told The Examiner that the document is a "preliminary report to be used in conjunction with and read within the context of all the reports and totality of the data available to us." The statistics, she said, are subject to change "for a variety of reasons, including late reporting, reclassification of some offenses, and discovery that some offenses are unfounded."

Lanier said when all classifications of sexual assaults are accounted for, including misdemeanors, there has been more than a 3 percent decrease when compared with last year. She did not elaborate when pressed to provide specific data showing the decline in sexual assaults.

Police union chief Kris Baumann said Lanier's formulation is designed to hide the number of serious violent sexual assaults.

"Sexual assaults are on the rise," he said. "If the department had aggressively informed the public of the danger, some people may not have become victims."

The difficulty is that there's different ways of measuring crime, said D.C. Councilman Phil Mendelson, whose committee has oversight of the police department.

There's always a conflict between the D.C. crime statistics the police department releases and those reported by the FBI. At the end of 2008, Lanier reported to the D.C. Council that violent crime had fallen over the previous year. When the FBI's uniform crime statistics came out in September 2009, they showed the number of murders, rapes, robberies and assaults had increased by 2.3 percent in 2008 from 2007.

Mendelson is sending a letter to Lanier that will "make the point that there needs to be a better explanation of these numbers."

Lanier said she's committed to providing "full and complete" crime information.

"If anything," she said, "more confusion arises because we do provide data in a variety of formats that allows people to analyze the data themselves."