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Helmets, Children, Bicycles and Injury Reductions in the US

Riding a bicycle with a helmet

Markowitz & Chatterji (2015) study the effects of what they refer to as the enactment of bicycle helmet laws in various states and localities in the United States laws on injuries requiring emergency department treatment.

In the abstract to the paper, the authors state:

Using hospital-level panel data and triple difference models, we find helmet laws are associated with reductions in bicycle-related head injuries among children. However, laws also
are associated with decreases in non-head cycling injuries, as well as increases in head injuries from other wheeled sports. Thus, the observed reduction in bicycle-related head injuries may be due to reductions in bicycle riding induced by the laws.

However a closer read of the paper does not in my view, fully support this conclusion … I would suggest and I believe the authors do acknowledge this, that they are drawing a bit of a long bow here. Still a paper worth having a read of if you can get a copy. It is behind a paywall.

Key Summary – Children and Bicycle Helmet Related Injuries

In the conclusion to the paper, Markowitz & Chatterji (2015) state:

To what do we attribute the observed changes in head and other injuries? Unfortunately, it is difficult to identify the mechanisms at work with our injury data, since we cannot distinguish between a decrease in riding versus a change in safe riding behaviors. Our results fit both stories.

That is, if the laws decrease bicycle riding we would see a decrease in both head injuries and injuries to other body parts, which we do. If the helmet laws promote safer riding practices in general and awareness of the risks of riding, we would also see the decrease in both head and non-head injuries. Our evidence in support of the decrease ridership theory comes from the observed increase in injuries in other wheeled sports that is associated with the bicycle helmet laws. We note that Carpenter and Stehr (2011) also find some evidence of the substitution effect using survey data on bicycle riding among high school students.

The uncertainty surrounding the mechanism at work also extends to the question of whether the laws themselves are responsible for the reduction in injuries, or rather, we are observing the effects of education campaigns, or changes in attitudes towards risk that accompany the helmet laws. As we noted earlier, the enforcement and penalties may vary widely across localities so where these factors are lax, the laws may have less to do with the reductions in injuries than the safety awareness that accompany the passage of the laws.

The mechanism aside, perhaps what is most important is an estimate of the total effect on injuries associated with the helmet laws. Considering the different offsetting results, we run our preferred specification on injury counts for 1) all head injuries and 2) total (all head and body) injuries arising from cycling and wheeled sports.

The net effects of the helmet laws are small and are not statistically different from zero. However, they do point to a net reduction, be they imprecisely estimated, with a 6 percent reduction in all head injuries and a 2 percent reduction in total injuries (results not shown).

The findings from this paper indicate that while bicycle helmet laws are widespread and thought to be effective, the net effect of these laws on health outcomes is actually not straight-forward. It is clear that there are offsetting behaviors and unintended consequences of these laws, and these effects need to be considered by policymakers.

The full reference for the paper is:

Markowitz, S. & Chatterji, P. (2015). Effects of bicycle helmet laws on children’s injuries. Health Economics, 24. 26-40

Other studies related to bicycle helmets are listed in the Cycling Research page.

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