Dennis J, Potter B, Ramsay T & Zarychanski R. Injury Prevention 2010;16:219-24
This paper presents data on helmet wearing and cycle use from the Canadian Community Health Survey (CCHS) between 2000 and 2007.
The original abstract reads:
Results: Helmets were reportedly worn by 73.2% (95% CI 69.3% to 77.0%) of respondents in Nova Scotia, where legislation applies to all ages, by 40.6% (95% CI 39.2% to 42.0%) of respondents in Ontario, where legislation applies to those less than 18 years of age, and by 26.9% (95% CI 23.9% to 29.9%) of respondents in Saskatchewan, where no legislation exists. Though legislation applied to youth in both Ontario and Nova Scotia, helmet use was lower among youth in Ontario than among youth in Nova Scotia (46.7% (95% CI 44.1% to 49.4%) vs 77.5% (95% CI 70.9% to 84.1%)). Following the implementation of legislation in PEI and Alberta, recreational and commuting bicycle use remained unchanged among youth and adults.
Conclusions: Canadian youth and adults are significantly more likely to wear helmets as the comprehensiveness of helmet legislation increases. Helmet legislation is not associated with changes in ridership.
The authors therefore conclude that provincial helmet legislation in Canada has not led to the sharp declines in cycling that were seen in Australia and New Zealand following enforcement of cycle helmet legislation (Robinson, 1996; NZMT, 2008b).
The data presented do not support these conclusions. There are in fact sharp falls in cycling after legislation evident in the data, which the authors do not draw attention to. They also assume a causal relationship between legislation and helmet use, but this assumption is unsafe. Experience shows that helmet laws will only impact long term helmet use and cycling levels materially if they are enforced.
The authors' summary of evidence on helmet effectiveness is consistently biased towards studies supporting one view. Unreliable results from case-control studies are put forward whilst later population-level studies are ignored. The population-level studies showed no evidence of serious injury reduction due to mass helmet use. It is now recognised that the case-control studies that make up the Cochrane Review were seriously confounded by social factors.
The authors do present data showing that cycling is a safe activity, yet they fail to ask the obvious question: if cycling is not an unduly risky activity, why are bicycle helmet laws being passed at all?
It is noted in the first paragraph that cycling is a popular physical activity in Canada, yet it causes only 2% of hospital injuries. This is good evidence that cycling is "safe" by the everyday standards of the word, and that cycle helmet promotion, let alone legislation, is disproportionate. The authors fail to recognise this point, yet it is fundamental to understanding whether cycle helmets are an appropriate response to those injuries that do occur.
The authors first present evidence to link helmet wearing rates with legislation. They take the examples of Nova Scotia, Ontario and Saskatchewan, respectively provinces with all-ages legislation, under 18's only and no legislation. Their analysis shows a progressive trend to higher rates of helmet use with more stringent legislation.
The limitations of the evidence should have been stressed. The authors are relying on self-reporting of helmet use in a survey based on telephone cold-calling. They do not draw on any data from street surveys, although these are available for several provinces. They do acknowledge in the discussion that self-reporting bias in legislation provinces could be an issue.
The authors make a serious error of logic by assuming a causal relationship between legislation and helmet use. Data not presented show that in Ontario, helmet use increased temporarily after the Under-18's law came into force in 1995, but after a few years returned to pre-law levels (Macpherson et al, 2006). The legislation was thus ineffective in altering helmet wearing rates in the long term. This might be because children cannot be charged for not wearing a helmet; only parents can be charged with permitting their children to ride without a helmet. The Toronto police never issued a single ticket for a helmet violation (Macpherson, 2004b) and indeed, beyond a temporary period of "stern warnings", ceased enforcing the law. So, at least with regard to child helmet laws, cause and effect between legislation and helmet wearing rates cannot be assumed since enforcement was not reliable.
The authors then study bicycle ridership, but in different provinces from helmet use: Prince Edward Island (PEI) and Alberta. This is an important shortcoming in their analysis, since they fail to show what effect helmet legislation had on wearing rates in those provinces. In addition to that problem, the ridership data presented in this section is particularly weak. Their ridership data are based on telephone surveys in which respondents were asked whether they had cycled in the last three months. If they had, they were classed as bicyclists. They were then asked how many times they had cycled in the last three months. This cannot be considered as robust data on ridership.
Although the authors claim that ridership was not affected by legislation, the data do not support such a conclusion. Indeed, the data are so poor as to be directly contradictory in some cases. For instance:
Despite these contradictions in the data, the authors conclude "We did not find a significant reduction in bicycle use among youth or adults following the implementation of legislation and even found an increase in bicycle use among Alberta youth in the year immediately following the introduction of legislation".
This is not a fair summary of the evidence presented.
Notwithstanding the conclusions of the authors, there is ample evidence in the literature that provincial helmet laws in Canada have reduced the amount of cycling. For example:
As already noted, the authors report that cycling is a popular activity in Canada, yet it causes only 2% of trauma admissions. One wonders why the authors failed to recognise the implications of that statistic. Clearly the risks of cycling are very low.
Risk in cycling was never studied at the time that helmet programmes began, in the 1970's. Cycling was assumed to be dangerous because many prominent cyclists said it was dangerous. The assumption was repeated so often that it became accepted as fact. In recent years, researchers have analysed available evidence to produce risk assessments. These have been for Europe, where data on bicycle use is available in varying degrees. For instance, Britain has good cycle use data going back more than 40 years. The risk assessments show that utility and leisure cycling are low-risk activities. That is to say, typical risks faced by cyclists are between 0.3 and 0.5 fatalities per million hours' use, which is within the range faced by drivers and pedestrians (Wardlaw, 2002). More intriguingly, since the early 1970's, the risks of cycling have fallen just as much as the risks of driving have. This effect pre-dates helmet use, and in fact has been compromised by helmet use, since helmet programmes deter cycling. Reduced cycling means more risk per cyclist.
Cycling is certainly not a high risk mode of travel like riding a motorbike, except possibly in competition.
The authors cite the Cochrane Review of bicycle helmet effectiveness in support of the view that helmets are effective to prevent serious head injuries. They ignore studies carried out in Australia and New Zealand that found no evidence that mass helmet use had changed the risk of serious head injury in a crash (Robinson, 2006).
Citing only half the evidence reveals lack of rigour. In the case of cycle helmet effectiveness, the contradiction of the evidence can be explained. The early case control studies, such as those that make up the Cochrane Review, were confounded by social factors. A more detailed analysis is presented by the Transport and Health Study Group (THSG, 2011). The Cochrane Review results show a systematic error, although this has been overlooked by the proponents of helmets. In brief, those of lower social status are unlikely to wear a helmet but are most likely to suffer serious head injury. This means that a natural helmet effect emerges simply from differences between social groups. In contrast, the failure of a whole population to see an improvement with 85% rate of helmet use is hard to explain away.
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