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Bicycle helmet prevalence two years after the introduction of mandatory use legislation for under 18 year olds in Alberta, Canada

Hagel BE, Rizkallah JW, Lamy A, Belton KL, Jhangri GS, Cherry N, Rowe BH.
Injury Prevention, 2006;12:262-265.

Summary of paper (Authors' abstract)

Objective: To determine changes in helmet use in cyclists following the introduction of a bicycle helmet law for children under age 18.
Methods: Cyclists were observed by two independent observers from July to August 2004 (post-legislation) in Edmonton, Alberta. The data were compared with a similar survey completed at the same locations and days in July to August 2000 (pre-legislation). Data were collected for 271 cyclists in 2004 and 699 cyclists in 2000.
Results: The overall prevalence of helmet use increased from 43% (95% CI 39 to 47%) in 2000 to 53% (95% CI 47 to 59%) in 2004. Helmet use increased in those under 18, but did not change in those 18 and older. In the cluster adjusted multivariate Poisson regression model, the prevalence of helmet use significantly increased for those under age 18 (adjusted prevalence ratio (APR) 3.69, 95% CI 2.65 to 5.14), but not for those 18 years and older (APR 1.17, CI 0.95 to 1.43).
Conclusion: Extension of legislation to all age groups should be considered.

BHRF Commentary

No evidence of injury reduction
The authors state that because the helmet law increased the proportion of cyclists wearing helmets, legislation should be considered for all age groups. However, head injury rates are not mentioned. Another source has claimed that across 9 health regions in Alberta head injuries doubled from 5% to more than 10% of cyclist injuries in the 6 months following introduction of the law, though this may have been due partly to changes in the way data were coded [5].

Several other studies (e.g. [6] [7]) have shown that, despite large increases in helmet wearing, enforced laws have had little effect on head injury rates, but have detrimentally affected public health by substantially reducing the amount of cycling. It is therefore strange that the authors recommend new helmet laws, without any evidence that existing legislation has been effective in decreasing head injuries.

Wrong basis for adult law proposal
To support their recommendation that the present Alberta helmet law should be extended to all age groups, the authors refer to data from Toronto of child cyclists under 15 years of age [10] and state that children riding with helmeted adults are almost 10 times more likely wear a helmet than children riding with non-helmeted children. A more appropriate comparison, though, is between children riding with helmeted and non-helmeted adults. In Toronto, children were just under 2.5 times more likely to wear a helmet when riding with helmeted adults.

However, later and more relevant data are available from Alberta itself [11]. These show that 99% of children wear helmets if their adult companion is helmeted and 84% if not. Thus children are only 1.18 times more likely to wear a helmet riding with a helmeted adult. This is very much less than the 10 times suggested by the authors using less relevant data.

Bias in selection of evidence on helmet benefits
Two references are cited in support of helmet effectiveness but the second [2] examined an exclusive subset of the same papers considered by the first [1]. Moreover, the second authors' own work dominated both analyses. There is no acknowledgement that these analyses have been widely criticised for bias, nor is there any reference to any paper sceptical of helmet effectiveness.

The suggestion that helmets reduce fatal injuries by 73% is particularly unsound. The cited reference simply presents an odds ratio of 0.27 without any attempt to adjust for confounders. More robust data based on whole populations and research specifically targeted at cyclist fatalities has failed to show any significant benefit from cycle helmets in preventing deaths [3]. In any case, NEISS data suggests that fewer than half (45%) of bicyclist deaths are due to head injury [4], so how could helmets possibly reduce fatalities by as much as 73%?

Conclusion
The data presented in this paper strongly suggest that Albert's child helmet law has led to a large decrease in cycling by children and teenagers, but this outcome is not even mentioned by the authors. Similarly the authors provide no evidence as to whether the law has been successful in reducing the risk of head injury.

The methodology used for the study is weak and its scope too selective. In the absence of strong evidence that the present law has been beneficial in reducing head injuries to cyclists (this paper provides no evidence of any benefit), the authors' conclusion is not justified. If the only outcome of the law has been to reduce cycling, it would be logical and in the interests of public health to recommend that the law should be repealed.

References

[1] Attewell RG, Glase K, McFadden M. Bicycle helmet efficacy: a meta-analysis. Accident Analysis & Prevention, 2001-05 v33 n3 p345-52.
[2] Thompson DC, Rivara FP, Thompson RS.. Helmets for preventing head and facial injuries in bicyclists (Cochrane Review). Cochrane Database Syst Rev, issue 4, 2002.
[3] see: What evidence is there that cycle helmets save lives?
[4] see: NEISS data on bicyclist injuries.
[5] see: Head injuries up after helmet law?
[6] Robinson DL. Do enforced bicycle helmet laws improve public health?. BMJ, 2006;332:722.
[7] Ji M, Gilchick RA, Bender SJ. Trends in helmet use and head injuries in San Diego County: The effect of bicycle helmet legislation. Accident Analysis & Prevention, 2006;38(1):128-134.
[8] see: The health benefits of cycling.
[9] see: How helmet promotion and laws affect cycle use.
[10] Khambalia A, Macarthur C, Parkin PC. Peer and adult companion helmet use is associated with bicycle helmet use by children. Pediatrics, 2005;116(4):939-942.
[11] Bicycle Helmets Observational Study Summary. Alberta Centre for Injury Control and Research, c.2001.

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