More to the point, detractors contend that helmets make biking seem like too much of an ordeal, a perilous endeavor. Intimidation, of the process, means fewer bikers.

Cities like Washington, D.C., have great bike-share systems, where bicycles are everywhere for the taking. Decisions to hop on a bike are often impromptu. Who among us is never without a helmet? Or wants to carry one all day after a one-way ride—which is a common use of bike shares. Guilt, and safety concerns that surround helmet-less biking, make many in that situation choose to drive instead. Is that better?

In Pinka Chatterji and Sara Markowitz's report for the NBER last week, they note that no nation-wide study in the U.S. has evaluated the effects of bike helmet laws on injuries. They also say that only one study has looked at helmet laws' effect on mortality—in it, they were "associated with a 15 percent reduction in fatalities among juveniles." Their complete report is worth reading if you care to go in depth on the statistics. In short, they found that in the U.S., kids and teenagers ride less in places with helmet laws, and suggest that less riding could be what actually accounts for reductions in bike-related injuries. They also get into how people are more aggressive on roller skates and skateboards when they're wearing helmets, which results in more overall injuries. They suggest that the same could be true for bicycles.

On that note, imagine we had to wear helmets while jogging. We would be safer. The helmets would inevitably save some lives, even if only by deflecting an occasional errant meteorite. But if we started ticketing all un-helmeted joggers, or giving stern looks to people running without helmets, what would that do for public health on the whole?

The NBER report comes on the heels of a thoughtful analysis by Elisabeth Rosenthal in the New York Times last fall, in which she discussed how European health experts justify cultures that use bicycle helmets much less than the United States:

... Yes, there are studies that show that if you fall off a bicycle at a certain speed and hit your head, a helmet can reduce your risk of serious head injury. But such falls off bikes are rare—exceedingly so in mature urban cycling systems. On the other hand, many researchers say, if you force or pressure people to wear helmets, you discourage them from riding bicycles. That means more obesity, heart disease and diabetes. And—Catch-22—a result is fewer ordinary cyclists on the road, which makes it harder to develop a safe bicycling network. The safest biking cities are places like Amsterdam and Copenhagen, where middle-aged commuters are mainstay riders and the fraction of adults in helmets is minuscule.

Manfred Neun, president of the European Cyclists Federation and outspoken helmet law detractor, made a similar point in The West Australian newspaper last spring, arguing that dedicated bike lanes and reducing car speeds in urban areas would do more to protect cyclists than helmets.