In their study of cycle helmet use and cyclist mortality in Ontario
[1], Wesson et al develop a statistical model that is claimed to show
helmet legislation led to a reduction in child cyclist deaths in Ontario.
This conclusion is not plausible, as may be demonstrated in two ways:
1. The legislation was never enforced [2] and had only a transient
effect. Helmet use by children increased only in the two years following
the law (1996 and 1997). Absence of enforcement allowed a fall back to pre
-law levels by 1999 with no change thereafter. The authors make the
statement near the end of the paper: "In the same urban community....
helmet use exceeded 65% in the 2 years after the introduction of
legislation and reached 85% in high income areas 6 years after the
introduction of legislation". This is an extract from full results that
have been reported [3]. The authors ought to have made clear that by 1999,
helmet use by Ontario children (all classes) had returned to pre-law
levels. This would have informed the reader that the statistical model was
invalid. Instead, the authors focused on a minority group in which helmet
use was not typical of the population. Adequate peer review would have
corrected this.
2. No control group was used. The decline in pedestrian deaths
closely correlates with the result for cyclists. Data from Ontario Road
Safety Annual Reports (ORSAR) [4] 1993-2004 show that deaths of children
declined steeply, both for cyclists and pedestrians, while adult deaths
declined only slightly. Due to the low number of cyclist deaths, the data
for cyclists are erratic, especially for children. The three year averages
for 1993-1995 and 2002-2004 were compared:
Child pedestrian deaths: -51%
Child cyclist deaths: -61%
Adult pedestrian deaths: -5%
Adult cyclist deaths: -13%
During these two periods, helmet use by child cyclists was the same,
as noted above. The very small number of child cyclist deaths by 2002-2004
(about 3 per year) means that the apparent advantage for cyclists cannot
be taken as significant. Similarly, adult cyclist deaths have large year
to year fluctuations, due to the low numbers (there were 178 adult cyclist
deaths during 1993 to 2004 inclusive, and 1,342 adult pedestrian deaths).
The authors' claim that the greater fall in deaths for child cyclists,
relative to adults, was due to helmet legislation clearly cannot stand
given that the same pattern was seen for pedestrians with no noted change
in helmet use. The large fall in deaths of children must therefore be due
to other factors, probably reduced exposure and street management
programmes to reduce vehicle speeds.
Actual Effectiveness of Helmets in Use
The authors support their conclusions with a discussion referring to
other evidence that apparently links helmet use to a reduction in deaths.
A number of emphatic statements are made. What is not explained is that
all the cited papers are case-control studies. In recent years, the poor
reliability of case-control studies, and systematic reviews based on them,
has caused disillusion in the epidemiology community [5, 6].
The only valid measure of whether helmets are effective is to examine
fatality and head injury data in populations where helmet use rose sharply
either due to promotion or enforced legislation. The outcomes in New
Zealand and the states of Australia were reviewed [7], and no noticeable
reduction in serious head injuries could be observed, after natural trends
and declines in cycling were accounted for.
For cyclist fatalities specifically, the evidence is alarming. In
Australia, cyclist head injury deaths fell by less than other road user
groups during the years when helmet legislation was enforced [8]. In the
United Kingdom, cyclists were the only road user group to see a sharp
increase in deaths after helmets first became popular in the mid 1990s
[9]. An extensive survey of US cyclist deaths also found a significant
link between helmet use and increased risk of death [10]. Since "reality
is the highest authority" to any serious person, it is surprising the
authors never mentioned these worrying developments.
The large discrepancy between case-control studies and the real-world
outcome is almost certainly due to socio-economic factors. It has been
reported that helmet wearing by children is strongly influenced by social
class, with children of low-income households being only 40% as likely to
wear a helmet, compared to children from high income households [3]. It is
also well recognised that children in low-income areas suffer
disproportionately from injuries inflicted by motor traffic [11]. The
confounding in the case-control research can be seen directly in this
summary drawn from the largest dataset ever gathered (3,900 casualties)
for a case-control study of cycle helmets [12]:
Protective effect of cycle helmet, Odds Ratios:
Against death Odds Ratio 0.07
Against severe brain injury Odds Ratio 0.24
Against brain injury Odds Ratio 0.33
Against any head injury Odds Ratio 0.32
These results apparently show that protective effect increases with
severity of injury. This is implausible and in any case is refuted - as
noted previously - by experience. However, this is the pattern that would
be expected if lower socio-economic class correlates - as it does - with
more severe accidents and not wearing a helmet. A large "helmet effect"
would be observed even with helmets of tissue paper.
This dataset forms the heart of the Cochrane Review of Bicycle Helmet
Effectiveness [13]. The review was carried out by the authors of the
original research. They have never commented on this aspect of their data.
Risk in Cycling
Wesson et al state: "Children are at risk for bicycle-related fatal
injuries". No data are presented to assess the risk relative to other
daily activities. Cycle helmet programmes and legislation have never been
justified by any evidence that cycling is hazardous or a major cause of
head injury. All such programmes rest for their credibility upon a deep-
seated stereotype that cycling is "dangerous". In fact, risk assessments
show that cyclists face everyday risks comparable to pedestrians and
drivers [14, 15]. In Canada, the rate of child head injury admission due
to cycling accidents is exceedingly low. National data (from CIHI) show
the annual rate was 11.5 admissions per 100,000 children per year in
1997/98 [16], or 1 case in 8,700 annually. This level of risk does not
justify helmet legislation, nor even promotion of helmets, at least not
for utility cycling.
Further analysis shows that the principal factor affecting risk is
the popularity of cycling [14, 17]; where cycle use increases, the risk
per cyclist decreases. The classic example of this was the boom in cycling
in the United Kingdom after the first oil crisis in 1973. During the
following ten years, national mileage cycled increased by 60%, yet cyclist
fatalities actually fell 10% during these years [18]. This "safety in
numbers" rule works in reverse too: less cycling means more risk per
cyclist. It has been found in Britain that the promotion of cycling is
linked to a reduction in cycle use [19]. Might this perverse result be due
to the prominence of helmets in all cycling promotion [eg: 20]? It is the
perfect illustration of incompetent policy that its actual effect is
directly contrary to the intended result.
Enforced helmet legislation has repeatedly been linked to large
declines in cycling and consequent increases in risk per cyclist. There
are many examples of this, but to cite only one, an all-ages helmet law
introduced in Nova Scotia in 1997 was followed by a 40-60% drop in the
number of cyclists counted [21]. Histories of the effects of enforced
helmet laws and strong helmet promotion are available [22].
Risk in not cycling
There appears to be very little appreciation of the health benefits
of cycling, or conversely, the danger in not cycling. Cycling has been
judged the most effective way of tackling the obesity epidemic, due to the
ease with which bike trips can become part of daily routine [23]. These
health benefits are substantial [24], being similar to giving up cigarette
smoking. The public health consequences of low cycling levels are large,
but are accepted as part of daily life. These include obesity, especially
child obesity, general low fitness levels, heavy suburban traffic
congestion, poor air quality, car dependency, lack of independent travel
by children, inter alia. To treat cycling as a "problem", requiring helmet
campaigns as a solution, is to perpetuate the stereotype of cycling as a
"dangerous nuisance". Competent public policy does not perpetuate
stereotypes, it is supposed to dispel them.
Conclusions
A large amount of evidence makes it clear that:
a) cycling is safe by everyday standards - helmet programmes harden
the stereotype that cycling is a high risk activity;
b) cycling gets safer as more people do it;
c) cycling is an extremely effective public health intervention,
comparable to discouraging cigarette smoking;
d) mass helmet use has never made cycling safer anywhere that it has
been tried; the only tendency noticeable has been an increase in deaths
and a decline in utility cycling.
References
1. Wesson et al. Trends in Pediatric and Adult Bicycling Deaths
Before and After Passage of a Bicycle Helmet Law. Pediatrics.2008; 122:
605-610.
2. Macpherson A, School of Kinseology, Toronto. Communication with
author, reporting City of Toronto Police Services advice that no child
cyclist was ticketed for violation of the helmet law. Dec 2005.
3. A KMacpherson, C Macarthur, T M To, M L Chipman, J G Wright, P C
Parkin. Economic disparity in bicycle helmet use by children si years
after the introduction of legislation. Injury Prevention 2006;12:231-235.
4. Ontario Road Safety Annual Reports. Various years. Available on-
line at:
http://www.mto.gov.on.ca/english/safety/orsar/
5. Lawlor D, Smith GD, Ebrahim S. Commentary; the hormone replacement
therapy – coronary heart disease conundrum; is this the death of
observational epidemiology? International Journal of Epidemiology
2004;33:464-67.
6. Smith GD. Classics in epidemiology; should they get it right?
International Journal of Epidemiology 2004;33:441-2.
7. Robinson D. Do Enforced Bicycle Helmet Laws Improve Public Health?
BMJ 2006;332:722-5.
8. Curnow WJ. The Cochrane Collaboration and Bicycle Helmets.
Accident Analysis and Prevention 2005;37:569-74.
9. Wardlaw M. Three Lessons For a Better Cycling Future. BMJ
2000;321:1581-5.
10. Rogers GB. Reducing bicycle accidents; a re-evaluation of the
impact of the CPSC bicycle standard and helmet use. J Product Liability
1988;11:307-17.
11. Edwards P, Green J, Lachowycz K, Grundy C, Roberts I. Serious
injuries in children: variation by area deprivation and settlement type.
Archives of Disease in Childhood 2008;93:485-489
12. Thompson DC, Rivara FP, Thompson RS. Effectiveness of bicycle
helmets in preventing road injuries. JAMA 276;1968-73.
13. Helmets for Preventing Head and Facial Injuries in Bicyclists.
Thompson DC, Rivara FP, Thompson RS. Cochrane Database of Systematic
Reviews 1999. http://www.cochrane.org/reviews/en/ab001855.html
14. Wardlaw M. Assessing the actual risks faced by cyclists. Traffic
Engineering and Control 2002;43:420-24.
15. "Cycling, Safety and Health", Krag T in European Transport Safety
Council Yearbook 2005.
http://www.etsc.be/documents/Yearbook_2005.pdf
16. Macpherson et al. Impact of Mandatory Helmet Legislation on
Bicycle-Related Head Injuries in Children - a Population-Based Study.
Pediatrics 2002;110:e60.
17. Jacobsen P. Safety in numbers; more walkers and bicyclists; safer
walking and bicycling. Injury Prevention 2003;9:205-9.
18. Department for Transport (UK state department). Road Accidents in
Great Britain; the Casualty Report. London. Years 1974-94.
19. Transport interventions promoting safe walking and cycling. The
National Institute for Clinical Excellence, 2006.
http://www.nice.org.uk/page.aspx?o=346196
20. Cycling to School. Web site of Cycling Scotland.
http://www.cyclingscotland.org/cyclingtoschool.aspx
21. Kreyes W. etc. Butting Heads Over Bicycle Helmets. CMAJ
2002;167:337-9
22. Helmet laws: what has been their effect? Bicycle Helmet Research
Foundation.
http://www.cyclehelmets.org/mf.html?1096
23. Report the UK House of Commons Health Committee. Obesity.
www.publications.parliament.uk/pa/cm200304/cmselect/cmhealth/23/23.pdf
24. Valuing the Benefits of Cycling. Cycling England. May 2007.
http://www.cyclingengland.co.uk/site/wp-content/uploads/2008/08/valuing-
the-benefits-of-cycling-full.pdf
Conflict of Interest:
None declared
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