A sharp-eyed reader wrote to the Post-Dispatch recently to ask why our St. Louis Crime Tracker shows Maplewood as having a negative number of rapes between March and August last year.

"This is clearly some sort of error," he said.

Strangely, negative crime totals are possible because of a method police departments use when counting crime to submit to the FBI's Uniform Crime Reporting program.

After investigating a crime, sometimes police departments need to reclassify it. Because crime reports can be delayed and investigations take time, these reclassifications can happen in a month later than the original crime.

Sarah Van Woert, a police analyst with the St. Louis County police, offered an example: "If in August a victim reported that someone broke into their home and stole a ring, that would be classified as a burglary," she said. But if in September "the officer discovered that the ring was stolen by a guest of the victim while they were allowed in the home, it would be changed to a larceny," because there wasn't any breaking and entering.