Thursday, May 24, 2012

Cyclists with helmets ride faster

Part of the perennial discussion about cycling helmets is whether wearing a helmet results in cyclists riding faster on average, thereby taking more risks and increasing the likelihood of injury.  The idea originates in the concept of risk compensation whereby people adjust their behavior until some level of risk is reached.  The classic example taught in economics is the Peltzman effect regarding seat belt use.  The hypothesis is that when seat belts were commonly installed in automobiles and used, drivers took more risks on the road thereby offsetting the increased safety of using the seat belt.  In my own teaching experience, many students had a hard time accepting this.  So I suggested a counter example -- not my idea by the way -- whereby a big spike is installed in the middle of every steering wheel pointing at the driver.  Would drivers on average be more careful?  If you think yes, then if people are willing to risk compensate when danger increases, why would the reverse be false?

The Wall Street Journal summarized some recent research on the topic regarding bicycle helmets ...
From 2009 to 2010, free bicycle helmets were issued to 1,557 volunteers in Bordeaux, France. The subjects' average age was 32 years; 58% were women. Previous helmet users were excluded.
Data was collected daily at seven locations, each equipped with two cameras programmed to detect moving objects, isolate cyclists and calculate their speed. Cyclists were photographed from above and behind.
Helmet use was recorded in 99, or 3.8%, of 2,621 movements made by 587 cyclists captured on camera.
Cycling speed of helmeted men averaged 11.9 miles an hour compared with 10.4 miles an hour for unhelmeted men. Helmeted and unhelmeted women cycled at 10.2 and 9.9 miles an hour respectively, suggesting risk compensation is a male behavior, researchers said. That behavior disappeared when helmeted men cycled in areas where speeds were extremely fast and the objective risk of injury increased, the study found.
There are some important caveats about the unobserved cyclists and whether they are meaningfully different from those observed in the data.  Moreover, it can certainly be the case that volunteers are inherently different from the rest of the population.  Nonetheless, while this is a simple data point, it does support the notion that pushing for greater helmet use by cyclists is not necessarily welfare improving.

EDIT: The original article is gated and such that details of the experiment are fuzzy.  I can interpret the passage above a few ways that (subjectively) make the selection effects more or less relevant.

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