Since October, crime on MUNI has dropped more than 30 percent. That's great news. As the Chronicle reports, the most impressive drop is in smart phone theft, which has fallen 77% from last May.
The San Francisco Police Department credits an increase in uniformed officers on trains for the decrease, as well as a public campaign—"Eyes up, phones down"—to keep members of the public alert. And it's hard to say that campaign hasn't had an effect.
But is it the whole story? Shouldn't a drop in phone prices lead to a drop in thefts? How much credit is due to the police, and how much to outside trends?
After all, criminals target smart phones partly because they're valuable. Nobody's snatching that battered copy of Infinite Jest with three bookmarks in it that you lug around on the N line, hoping it will help you pick up girls. (Personal aside: It won't.)
So, if that's all true, then a drop in the price of smartphones should also lead to a drop in smartphone thefts.
In the last year, the worldwide average price of a smartphone dropped almost ten percent—from $335 in 2013 to $308 in 2014. It's predicted to keep dropping too, leading some observers to predict that "dirt cheap smart phones are the wave of the future." So it's at least plausible that part of the drop in crime isn't being caused by the increase in police—but changes in prices.
(If you want to really get into the data weeds, it could also just be what statisticians call a "regression to the mean." Given one highly-outlying measurement there's a strong possibility that the next measurement will tend to return towards the underlying average. It's the same as children of very tall or very short parents are likely to be themselves—while still tall or short—closer to the average. Likewise, our crime rate spiked to a five-year high in 2013, giving a strong chance of predicting a drop in the next sample.)
But hey, good is still good news. Get to work safely today—and good luck finishing Infinite Jest.