Another article has appeared claiming to be the final say in the debate about repeal of mandatory bicycle helmet laws in Australia. The research paper, entitled “The impact of compulsory cycle helmet legislation on cyclist head injuries in New South Wales, Australia” has received some media coverage at the ABC, News Limited and Fairfax Media.
In this report* the authors claim to have identified evidence that compulsory helmet laws reduced head injuries by between 25% and 29% when they were introduced in NSW in 1991. In their conclusion, they state:
“Despite numerous data limitations, we identified evidence of a positive effect of compulsory cycle helmet legislation on cyclist head injuries at a population level such that repealing the law cannot be justified.”
Perhaps what is most telling about this statement is how quickly the authors are willing to jump from their findings about reductions in head injury rates in 1991 to an assertion that this piece of evidence alone is enough to justify mandatory helmet laws today.
What many advocates of MHLs seem unable or unwilling to comprehend is that head injury reduction (in the event of a crash) is just one of the many factors which is relevant to the debate surrounding whether our mandatory helmet laws are a good idea. Injury reduction is a necessary but far from sufficient condition for justifying compulsion. If reduction or elimination of injury was the only relevant consideration then the simplest and most effective thing to do this would be to ban bicycles altogether.
In reality numerous other things are relevant to the issue:
- Do MHLs make riding a bike less appealing and hence reduce the number of cyclists?
- Is it possible that MHLs actually increase the likelihood of having a crash (through risk compensation and reduced safety in numbers)?
- Have MHLs and the accompanying government promotion of helmet use at all times created an exaggerated belief in the effectiveness of helmets in preventing injury or death in the minds of cyclists and motorists?
- Perhaps most importantly; is the absolute level of risk to an individual riding helmetless great enough to warrant any sort of intervention from government in the first place?
None of these topics are addressed by the authors, but fortunately for us, some people are considering the questions that the safety experts refuse to.
Not only is the scope of the study just too narrow to support their sweeping conclusion that repeal of the law in unjustified, the evidence presented for the case that helmet laws have significantly reduced injury is far from compelling.
The study examined the ratio of head injuries to arm (and leg) injuries during a 3 year period around the time the law was enacted in NSW on the basis that if the law was effective a decline in the ratio of head injuries to other types of injuries should be evident, similar to the approach of the now discredited Rissel paper (2010) . However the study made no effort to control for any change in the number of cyclists following the introduction of the law, hence any observed improvement in the injury rate can only be interpreted as evidence for a reduction in head injuries relative to limb injuries and not as a outright reduction in the rate of head injury per cyclist.
Many researchers agree that cycling numbers declined meaningfully following implementation of helmet laws in Australia, something which the report’s authors acknowledge when they state in their introduction:
“A decrease in cyclist numbers among those aged under 16, predominantly among teenagers, was observed in the years immediately following the legislation in both Victoria and NSW.”
Other research has concluded this effect was not confined to younger riders and that the number of people (both adults and children) riding bikes declined by as much as 30% or 40% after the laws were introduced across the various Australian states and territories. Given reductions in cycling of this magnitude, it is entirely possible that the risk and incidence head injuries to each cyclist was in fact unchanged or even increased as a result of helmet legislation.
Aside from the fact that the study did not control for a change in cyclist numbers, there are two other important observations which draw its results into question.
Firstly, the authors have not provided evidence that the decline in the ratios of head injuries to limb injuries was actually due to the introduction of the helmet law. They state:
“We have assumed that the additional decrease in head injuries at the time of legislation was attributable to the legislation; however, it is not possible to infer causality with certainty without having helmet wearing data on all cyclists.”
It seems strange that a study intended to assess the effectiveness of the legislation would simply assume it be effective. And there is ample reason to at least question whether the reductions were not caused by other unrelated factors.
Even a cursory examination of the above graphs showing the month to month evolution in head-to-arm and head-to-leg ratios over time does not reveal an obvious and significant break at the time of the change in the law. Any effect appears very subtle at best. The series are also volatile with large monthly variations common, not just over the period following the law change. In fact for the data on head-to-leg injury rates the largest decline evident does not even occur at the time of the change in law. On both the graphs of head-to-arm and head-to-leg, the declines in ratios at the time of the law change are both preceded by large increases in the ratios in the month just prior, something not explained by the authors.
Secondly, any downward effects (such as they are) are not even persistent. The ratios of head-to-arm and head-to-leg injuries are both actually higher at the end of the 36-month period than they were at the start. This is acknowledged in the report:
“Based on the original analysis there is some evidence that the initial improvement in head injury rates diminished over the 18 months following legislation as shown by the increasing post-law head to limb injury ratios in Fig. 4.”
While the authors’ main analysis and conclusions are certainly unconvincing to us at Helmet Freedom, they are to be commended for making some comments about the need to keep the usefulness of helmet laws in proper perspective:
“While helmet legislation appears to play an important role in the reduction of cyclist head injuries, further improvements in cyclist safety in general may be gained from a broader focus. Cyclist safety is a complex issue driven by a range of factors….increased volume and quality of cycling infrastructure could improve safety, particularly for cycling commuters, through reduced competition for road space with motor vehicles.”
We could not agree more. Cycling safety is a complex issue, as is the question of whether mandatory helmet laws are a good thing or not. And unfortunately for anyone looking for the “smoking gun” evidence on MHLs, this report is not it.
If you feel that the justification for our helmet laws should be based on more than just one very narrow part of picture, please write a letter to your state MP and state transport minister. If we don’t tell them what we think, nothing will change. Feel free to include our critiques of these various studies to help bolster your point – our work is independent, unpaid & copyright free.
* Which was largely government-funded, including “core funding provided by the NSW Health Department, the NSW Roads and Traffic Authority and the Motor Accidents Authority”.