In any given year, more than 18,000 U.S. police agencies are asked to submit crime data to the FBI. But some don't provide complete information or, in some cases, any information at all.

When that happens, the Federal Bureau of Investigation uses crude estimates to account for the missing data. Those figures are then used to generate "Crime in the United States," an annual tally of violent and property crimes that is a quality-of-life measure as well as a gauge of criminal justice policies and spending.

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Other experts believe, at minimum, the FBI should use a more sophisticated system for generating estimates.

Two decades ago,  the Bureau of Justice Statistics, a unit of the Justice Department, published a 78-page paper critiquing the FBI's procedure and recommending ways to improve it.

"So far, nothing has come of it," said Michael D. Maltz, the criminologist who wrote the paper and is now a researcher at Ohio State University's Criminal Justice Research Center.