Intended for healthcare professionals

Analysis And Comment

Arguments against helmet legislation are flawed

BMJ 2006; 332 doi: (Published 23 March 2006) Cite this as: BMJ 2006;332:725

Conflicting Evidence

The authors' response is very selective in its presentation in order
to press their well known pro-helmet position. It begins by quoting
studies that support their views while curiously omitting any reference to
the many that don't. For example there is no reference to the study by
Rodgers [1] of 8 million cyclists in the USA that found "that the bicycle-
related fatality rate is positively and significantly correlated with
increased helmet use" in line with the findings of Robinson and others for
New Zealand and Australia. Neither is there a reference to the two recent
papers by Hewson [2,3] looking at UK police and hospital statistics which
found no difference in head injury rates in male and female children
despite the helmet wearing rate of the females being double that of the
males. In respect of adults and children Hewson stated "The conclusion
cannot be avoided that there is no evidence from the benchmark dataset in
the UK that helmets have had a marked safety benefit at the population
level for road using pedal cyclists"[3]

The authors reference, in support of their position, six
"independent" and mostly old studies (w1-w6). In one (w2) the authors have
agreed mathematical errors which when corrected revise the conclusion to
every helmet preventing two head injuries - a clear case of confounding if
ever there was one. Two more are the authors' own, one of which [4] is
the source one of the most quoted figures in favour of helmets - an 85%
reduction in head injuries. That study compared helmeted children, mostly
white, well-off, and cycling in parks, with unhelmeted children, mostly
black, cycling in busy urban streets and attributed the difference in head
injury rates to the helmet wearing. It has rightly been criticised for
lacking "scientific rigour" [5]. Yet that flawed figure has become the
rallying cry for much well meaning but misguided helmet legislation and
promotion across the world.

The authors point to Robinson's Fig 2 [6] as evidence of increased
helmet use reducing injury. However even a cursory visual inspection of
Fig 2 shows it would be impossible to identify the year that helmet use
doubled if Robinson had not helpfully marked it for the reader - indeed
most would guess it happened six years earlier in 1985 if not told

The authors dismiss the concept of risk homeostasis in helmet wearers
but conveniently omit reference to their own study that found that injured
children who had worn helmets reported they rode faster and suffered more
damage to their bikes than those without helmets [7]. There is also other
criticism of their "no risk homeostasis" case [8]

Whatever the truth about helmets, cycling is an extremely safe
activity with a lower head injury rate per km than walking. Head injuries
form a lower proportion of all child cyclist hospital admissions in
England (38%) than for child pedestrian admissions (44%). Cyclists
represent just 7% of all hospital head injury admissions exceeded by trips
and falls (42%) and even assaults (11%). Yet while the BMJ had published
many papers on cycling helmets I can only recall one (a tongue in cheek
paper with a serious message by Wardlaw [9]) suggesting helmets for
pedestrians. One has to wonder why cyclists merit singling out by the
medical profession for intervention with helmets. As the Netherlands has
demonstrated, you can achieve the lowest cyclist head injury rate in the
world with helmets being worn by only one in a thousand of your cyclists.

Even so, given the design limitations of cycle helmets (a design
maximum of a stationary fall from a height of 2m onto a flat surface) and
that 97% of cyclist accidents in London involve a motor vehicle it is
clear that this is an intervention with equipment whose design limits fall
well short of the overwhelming majority of cycling injury accident

Those who press us down the path of helmet compulsion in the face of
the clearly conflicting evidence risk a repeat of the mistakes made with
hormone replacement therapy [10].

Tony Raven

[1]Rodgers, G.B., Reducing bicycle accidents: a reevaluation of the
impacts of the CPSC bicycle standard and helmet use, Journal of Products
Liability, 1988, 11, 307-317.

[2]Hewson, P.J., Investigating population level trends in head
injuries amongst child cyclists in the UK, Accident Analysis &
Prevention. 2005;37(5):807-815

[3]Hewson P.J., Cycle Helmets and Road Casualties in the UK, Traffic
Injury Prevention, 2005;6(2):127-134

[4] Thompson, R.S., Rivara, F.P. and Thompson, D.C., A case-control
study of the effectiveness of bicycle safety helmets, The New England
Journal of Medicine, 1989 320(21) 1361-1365

[5]Curnow, W.J., 2005. The Cochrane Collaboration and bicycle
helmets. Accid. Anal. Prev. 37 (3) 569-574.

[6]Robinson D.L., No clear evidence from countries that have enforced
the wearing of helmets, BMJ 2006;332:722-725

[7]Mok D, Gore G, Hagel B, Mok E, Magdalinos H, Pless B., Risk
compensation in children’s activities: A pilot study; Paediatr Child
Health. 2004;9(5):327-330.

[8] Adams J, Hillman M, BMJ 2001;322:1063

[9]Wardlaw, M.J., Three lessons for a better cycling future. BMJ:

[10]Petitti D. Hormone replacement therapy and coronary heart
disease: four lessons. Int Journal of Epidemiology, 2004;33:461-463

Competing interests:
None declared

Competing interests: No competing interests

28 March 2006
Tony Raven
Cyclist & DPhil, Engineering Science
Cambridge SG8 6BN