There are many ways to measure crime, and all are open to dispute and manipulation.
So let's try something different. Does the amount of evidence tape purchased by the Baltimore Police Department tell us anything about whether the city is more or less dangerous?
I ask this only because the Board of Estimates approved this week the purchase of $17,490 worth of evidence tape. It was the low bid from the Lynn Peavey Co., which by the looks of its Internet site supplies everything needed to open a C.S.I. unit in your garage.
Yes, we're talking about the stickers that go on boxes and bags and other things collected at crime scenes that might be needed later for testing and trial.
So how much tape did the city buy?
It's hard to say. The head of the Police Department's Crime Lab wouldn't talk to me, and a representative from the company refused to be quoted by name.
Baltimore apparently bought 1 3/8 -inch-wide pressure-treated tape that changes ink color when it's tampered with. At the $13.95 listed for each roll on the Web site, the city could have bought 1,253 rolls, or 25.63 miles of evidence tape.
That's enough to wrap around a smidge under half of the 51.46 mile Baltimore Beltway.
Maybe we got a deal we couldn't pass up. Maybe police are solving more crimes and thus bag more evidence. Or maybe crime is so out of control that we're running out of office supplies needed to keep track of it.
The latest crime statistics released Wednesday by city police show that homicides are down 29 percent and shootings are down 13 percent so far this year. But thefts from cars are up 10 percent and burglaries are up by 4 percent.
In years past, it's been shootings and homicides that drive the numbers up, and city officials complained that the news media ignored drops in other categories that they said painted a more realistic picture of crime. This year, it's all about homicides, and if the trend continues through December, the year will no doubt be a resounding success for the Dixon administration.
So why not measure crime by the way police buy their supplies?
Because of course it's not always accurate. Sometimes a purchase is indicative of an unusual trend. Other times it's simply a routine, bulk order, as police spokesman Sterling Clifford said is the case with the evidence tape.
"It's the regular amount that gets purchased once or twice a year," he said. "I suspect if we were buying vastly more ammunition or handcuffs, that might raise an eyebrow."