A bicycle helmet is designed to attenuate impacts to the head of a cyclist in falls while minimizing side effects such as interference with peripheral vision * Population studies compare changes in helmet use and injury rates in a single population over time, most notably where helmet laws have resulted in large changes in a short time. A review of jurisdictions where helmet use increased by 40% or more following compulsion showed no measurable change to head injury ratesBritish Medical Journal. The largest study, covering eight million cyclist injuries over 15 years, showed no effect on serious injuries and a small but significant increase in risk of fatalityReducing Bicycle Accidents: A Reevaluation of the Impacts of the CPSC Bicycle Standard and Helmet Use Rodgers GB. 1988. Journal of Products Liability: 1988,11:307-317 . Weaknesses of this type of study include: simultaneous changes in the road environment (e.g. drink-drive campaigns); inaccuracy of exposure estimates (numbers cycling, distance cycled etc.).
Different analyses of the same data can produce different results. For example, Scuffham analysed data on the New Zealand helmet law in 1995 and concluded that, after taking into account long-term trends, the laws had no measurable effectTrends in cycle injury in New Zealand under voluntary helmet use Scuffham PA, Langley JD. 1997. Accident Analysis and Prevention: 1997 Jan;29(1):1-9. His subsequent re-analysis without accounting for the long-term trends showed a small benefitHead injuries to bicyclists and the New Zealand bicycle helmet law, Scuffham P, Alsop J, Cryer C, Langley JD. 2000. Accident Analysis and Prevention: 2000 Jul;32(4):565-73. Re-analysis of the Thompson, Rivara and Thompson data substituting helmet wearing rates from co-author Rivara's contemporaneous street counts, reduces the calculated benefit to below the level of statistical significance. Another analysis of the source data form this study showed a 70% reduction in lower limb injuries from helmet use. One problem with all analyses is that the population of injured cyclists is generally very small, and it is difficult to collect sufficient incidents to form a statistically signifciant sample.
The definition of injury is also open to debate, and injury figures are acknowledged to be inacurate. Research by TRL and others shows that reporting of injuries is inversely related to severity. Fatal injuries are almost always reported, in the developed world, but 90% or more of lesser injuries go unreported. Helmets are most likely to be effective against lesser injuries. Pro-helmet studies routinely refer to prevention of traumatic brain injury, which has connotations of permanent intellectual disablement, but where sufficient data is provided it is found that the majority of the brain injuries in these studies are concussion. A study of fatally injured cyclists found injuries of fatal severity to multiple organ systems were in sixteen of twenty riders, including six with no significant head injury. Four riders died of fatal injury to head alone and one of these was the only rider know to be wearing a safety helmet. His death resulted from a fall from a bicycle at moderate speed rather than collision with a motor vehicle.Fatal injuries to bicycle riders in Auckland. Sage MD. 1985. NZ Med J: 25 Dec 1985 Vol 98 No 793
Recent research on traumatic brain injury adds further confusion, suggesting that the major causes of permanent intellectual disablement and death may well be torsional forces leading to diffuse axonal injury (DAI), a form of injury which helmets cannot mitigateThe efficacy of bicycle helmets against brain injury, Curnow WJ. 2003. Accident Analysis and Prevention: 2003,35:287-292.
Much of the research is partisan in one way or another. Thompson, Rivara and Thompson were already committed advocates of helmet legislation before publishing their first study; their report for the Cochrane review has also been criticised for being dominated by their own work. Rodgers, who showed helmets to be associated with increased risk of fatality, was replying to criticism of CPSC for focusing on bicycle design and manufacture standards. One report concluding a 60% reduction in injuries was found to be in error due to a simple statistical error; correcting the error results in a claimed efficacy of 186%; despite this the authors continue to assert that the results standTrends in serious head injuries among English cyclists and pedestrians, Injury Prevention 2003; 9: 266-267 and responses. A report commissioned by the UK Government was supportive of cycle helmet promotionBicycle helmets - a review of their effectiveness: a critical review of the literature Towner E, Dowswell T, Burkes M, Dickinson H, Towner J, Hayes M. 2002. Department for Transport: Road Safety Research Report 30 but dismissed out of hand much of the contradictory evidence, and the principal authors were associated with a programme of the Child Accident Prevention Trust (CAPT), which is strongly pro-helmetCritique of Road Safety Research Report 30. Curnow, author of papers on helmets and traumatic brain injury, has also published criticism of pro-helmet researchThe Cochrane Collaboration and bicycle helmets Curnow WJ. 2005. Accident Analysis & Prevention: 2005;37(3):569-573.
There is a long-running argument over the use, promotion and compulsion of cycle helmets. Most heated controversy surrounds laws making helmet use compulsory, particularly regarding the substantial disparity between claimed injury savings in small-scale prospective studies (e.g. Thompson, Rivara and Thompson, 1989) and later, more comprehensive studies, particularly from jurisdictions which have used compulsion to substantially raise helmet use over a very short period. Helmet use in New Zealand, for example, rose from 43% to over 95% in under three years, with no measurable change in head injury rates (Scuffham, 1997).
Controversy is fuelled by support given to the pro-compulsion movement by Bell Sports in particularHelmet compulsion pressure group SafeKids acknowledges Bell Sports as a major sponsor., and by the fact that many of the most vocal proponents of helmets are not themselves cyclistse.g. Angela Lee, chief executive of British helmet pressure group the Bicycle Helmet Initiative Trust, interviewed in BikeBiz in 2003..
Various organizations have taken up definite positions on the issue, not always based on a full review of the evidence. For example, the British Medical Association used to be against helmet compulsion, following an extensive review of the evidence in 1999. In late 2004 the BMA's Board of Science and Education adopted a 'position' calling on the UK government to introduce cycle helmet legislation, and this was confirmed at the 2005 Annual Representative Meeting following fifteen minutes of debate(transcript). The BMA's new position use statistics provided by the British political lobby group, the Bicycle Helmet Initiative Trust, and exclude from consideration the majority of conflicting evidence, including the BMA's own previous work. Several provably wrong figures were removed after initial publication, but the review is still viewed as distorted, excluding not only references included in the 1999 BMA study, but the 1999 study itself. Debate continues within the BMA.
Overall, according to CTC, the UK's national cyclists organisation, "the evidence currently available is complex and full of contradictions, providing at least as much support for those who are sceptical as for those who swear by them."CTC position paper on helmets
Reduction in bicycle participation
Mandatory bicycle helmet laws may lead to a reduction in the number of cyclists. The reduction in the number of cyclists may have a more negative impact on the health of a population than would have arisen from the head injuries that would have resulted from not using helmets since the reduction in injuries is apparently so small. The long term health benefits of bicycle use are well established so any reduction in bicycle activity will likely have a negative impact on the overall health of a population.
According to the "safety in numbers" theory, decreased cycling may have a negative effect on the safety of the remaining cyclists.
Cycle helmet promotion or high levels of use may deter cycling by reinforcing the misconception that bicycling is more dangerous than traveling by passenger car [1]. Such a reduction in cycling might cause an increased risk for remaining cyclists due to a "safety in numbers" effect.
Helmets and risk of injury
Many believe that a helmet can save a cyclist's life, an idea which is repeatedly asserted in debate. There is no sound evidential basis for this claim and there are no known cases where mass helmet use has actually reduced the number of cyclists' deaths or serious head injuriesLetter from David Jamieson, MP, minister of state for transport, to Michael Jack, MP. Association with increased risk of death has been reportedBMJ 2000;321:1582-5. It is likely that helmets could prevent a significant number of minor cycling injuries but the overall safety benefits are inconclusive; this is thought to be in part due to risk compensation behavioure.g. Mok et al., Risk compensation in children's activities: A pilot study, Paediatric Child Health: Vol 9 No 5 May/June 2004John Adams, 1995, Risk, Routledge, ISBN 1857280687 â€" (Authoritative reference on risk compensation theory.)Death on the Streets: Cars and the mythology of road safety, Davis, 1993, ISBN 0948135468. A cost-benefit analysis of the New Zealand helmet law showed that the cost of helmets outweighed the savings in injuries even taking the most optimistic estimate of injuries preventedNew Zealand bicycle helmet law-do the costs outweigh the benefits? Taylor M, Scuffham P. 2002. Injury Prevention: 2002;8:317-320 .
While a helmet may mitigate the effects of a fall or collision, other factors (such as maintenance, road conditions, and driver behaviour) are more important for reducing the chance of such accidents in the first place. In general, the value of bicycle helmets has been systematically overstatedHansen P, Scuffham PA, Aust J Public Health: 1995 Oct;19(5):450-4.
Some studies have even suggested that helmets increase risk. Although the head injury rate in the US rose by 40% as helmet use rose from 18% to 50%, this does not necessarily mean that helmets themselves increase risk. In fact, a range of theories exist to explain the observed disparity, including: * Risk compensation: helmeted cyclists may ride less carefully; this is well supported by evidence for other road safety interventions such as seat belts and antilock brakes. * Poor fitting * Sampling bias in prospective studies: voluntary wearers may be more risk averse, skewing the results.
No research has yet been published which adequately addresses the reasons for the disparity.
Promotion and compulsion
Helmet use has increased significantly in many, but not most, jurisdictions since the 1980s, primarily because of helmet promotion and compulsion laws. The following countries have mandatory helmet laws for either minors only, or for all riders: Australia, Canada, Finland, Iceland, New Zealand. In the U.S. 21 states have mandatory helmet laws. An analysis of helmet laws in the British Medical Journal showed that these laws have failed to yield measurable reductions in head injuries. The major documented effect of helmet laws is to reduce cycle use.
Use of cycling helmets is supported by numeorus groups including the United States American Medical AssociationAMA and the National Safety Council. According to the NSC, head injuries cause 85 percent of bicycling fatalities, although it is unclear whether this is markedly different than for all trauma fatalitiesNSC.
It is plausible that if a rider chooses to use a helmet, and maintains their safe cycling habits, they should be moderately safer than if they chose not to wear a helmet, although risk compensation theory states that an intervention as obtrusive as a helmet will very likely affect riding practice at the subconscious level. Wearing and non-wearing are both, therefore, sound choices, supportable from the available evidence. A person refusing to ride without one probably overestimates either the risks of cycling or the protective effect of helmets.
Promotion of helmets is somewhat more problematic. Helmet promoters routinely make claims which manufacturers cannot, due to advertising restrictions. Promotion campaigns are often supported and/or funded by manufacturers. Bell, one major helmet manufacturer, supports both helmet promotion and, through its Legislative Assistance Programme, laws. The major problem with helmet promotion, from the point of view of cycle activists, is that in order to present the idea of a "problem" to match the solution they present, promoters tend to overstate the dangers of cycling. Cycling is, according to the evidence, no more dangerous than being a pedestrian. In fact, helmet compulsion in cars would be far more effective at reducing injuries than on bicycles. [2]
Some bicycle activists complain that focus on helmets diverts attention from other issues which are much more important for improving bicycle safety, such as training, roadcraft, and bicycle maintenance. Of 28 publicly funded cycle safety interventions listed in a report in 2002, 24 were helmet promotions. For context, one evaluation of the relative merits of different cycle safety interventions estimated that 27% of cyclist casualties could be prevented by various measures, of which just 1% could be achieved through a combination of bicycle engineering and helmet use.
Data from around the world shows that despite the optimistic claims for injury reduction made by their proponents, no helmet law currently in force has led to a measurable reduction in cyclist head injury rates. There are a number of plausible explanations for this: * the studies on which the laws are founded mainly compare those who choose to wear helmets with those who do not; forcing a cyclist to wear a helmet will not make them behave like the kind of cyclist who wears one by choice * helmets are not designed to withstand motor vehicle impacts, but these account for most serious and almost all fatal cyclist injuries * governments do not tend to measure minor injury rates; any protective device would be expected to be much more effective against minor injuries, rapidly tailing off with severity - although a few studies do claim that cycle helmets are more effective against serious than against minor injuries, it is more likely that the efficacy figures cited in advance are against a type of injury which subsequent statistics will not measure * helmet laws tend to deter cycling; the theory of safety in numbers asserts that cycling becomes safer the more people who do it.
Cycling as a dangerous activity
A further source of contention is the apparent arbitrariness of cycle helmet promotion and/or compulsion. Ordinary cycling is not demonstrably more dangerous than walking or drivingTraffic Engineering & Control Dec 2002 pp352-6, yet no country promotes helmets for either of these modes (although there was an experiment in Japan with walking helmets for children, which demonstrated no measurable benefit). Cycle helmet use correlates inversely with the level of cycling in a given country. Official zeal for cycle helmets is greatest where cycling is a minority activity.
Detailed analysis of hospital admissions data also fails to support the idea that cycling is unusually dangerous: a study in the UK found that the proportion of cyclist injuries which are head injuries is lower than the proportion for pedestrians at 30.0% vs. 30.1%.
Overall, cycling is beneficial to health - the benefits outweigh the risks by up to 20:1Hillman, 1999 . Anything which jeopardises that benefit must be carefully weighed to ensure it is likely to achieve some meaningful benefit in turn. Thus far, no helmet law has been shown to do that.
* Thompson, R., Rivara, F. and Thompson, D. (1989), A Case-Control Study of the Effectiveness of Bicycle Safety Helmets, New England Journal of Medicine, 25 May, 320:21, 1361-67 Abstract — (The most widely cited pro-helmet study.) * Bicycle Helmet Research Foundation, "Commentary on A Case-Control Study of the Effectiveness of Bicycle Safety Helmets", accessed 21st June 2006 * Scuffham Trends in cycle injury in New Zealand under voluntary helmet use, Langley. Accident Analysis and Prevention, Vol 29:1, 1997 &mdash (Showed no benefit from large-scale increases in helmet use.) * John Adams, 1995, Risk, Routledge, ISBN 1857280687 — (Authoritative reference on risk compensation theory.)
Helmet Fit
* Parkinson, Gregory and Hike, Kelly E. (2003), Bicycle Helmet Assessment During Well Visits Reveals Severe Shortcomings in Condition and Fit, [3] Pediatrics, 2 August2003 Vol. 112 No. 2, pp. 320-323 — (Showed that correct fitting is an exception.)
* BikeBiz (industry journal), "Helmet battle flares up in BMJ", March 24th 2006 * BikeBiz (industry journal), "Let's fight for our rights to the road, argues CTC", Feb 27th 2006 * British Medical Association, "Legislation for the compulsory wearing of cycle helmets", November 2004 * D Hendrie, M Legge, D Rosman, C Kirov, "An economic evaluation of the mandatory bicycle helmet legislation in Western Australia", Road Accident Prevention Research Unit, Department of Public Health, The University of Western Australia. * Hagel, Macpherson, Rivara, Pless, "Arguments against helmet legislation are flawed"Br med J, 2006;332:725-726 (25 March), doi:10.1136/bmj.332.7543.725 * Merton, R.K., "The Unanticipated Consequences of Purposive Social Action", American Sociological Review, Vol.1, No.6, (December 1936), pp.894-904. (see Unintended consequence) * Scuffham, Alsop, Cryer, Langley, "Head Injuries to Cyclists and the New Zealand Cycle Helmet Law", Accident Analysis and Prevention, 2000, 32: 565-573 * Vulcan, A.P., Cameron, M.H. & Heiman, L., "Evaluation of mandatory bicycle helmet use in Victoria, Australia", 36th Annual Conference Proceedings, Association for the Advancement of Automotive Medicine, Oct 5-7, 1992. * Vulcan, A.P., Cameron, M.H. & Watson, W.L., "Mandatory Bicycle Helmet Use: Experience in Victoria, Australia", World Journal of Surgery, Vol.16, No.3, (May/June 1992), pp.389-397.
