No clear evidence from countries that have enforced the wearing of helmets
BMJ 2006; 332 doi: https://doi.org/10.1136/bmj.332.7543.722-a (Published 23 March 2006) Cite this as: BMJ 2006;332:722
All rapid responses
It was a pleasure to read all the different contributions, especially Dan Hicks's interesting and relevant point that most US cycling organisations do not support helmet laws because the health benefits of cycling outweigh the risks of riding without a helmet.[1]
Cycling organisations also oppose helmet laws because they reduce Safety in Numbers. Countries with low helmet wearing rates have more cyclists and lower fatality rates per cycle-km. Fig 1 shows that a non-helmeted cyclist in Denmark or Holland is many times safer per cycle-km than a helmeted cyclist in the US. This pattern is also reflected in injury statistics. US cyclists with 38% helmet wearing suffer 30 times as many injuries per million cycle km as Dutch cyclists with 0.1% helmet wearing.[2]
Thus at best, the benefits of helmets are too small to be apparent in across-country comparisons. At worst, helmet laws reduce Safety in Numbers and distract attention away from what’s really important, reducing the risk of bike/motor vehicle collisions, the cause of the majority of debilitating head injuries to cyclists.[3]
The potential to do more harm than good means that helmet laws must be evaluated with the utmost care. Evaluations should estimate the effects on cycle use, safety in numbers and risk compensation. They also need to separate the effects of increased helmet wearing from gradual trends inherent in time series data. My review achieved this by considering jurisdictions where legislation increased percent helmet wearing (%HW) by more than 40 percentage points within a year. Such large increases in %HW in a short time period should produce obvious responses in head injury rates if helmet laws are beneficial.
Diane Thompson argued that this criterion "ignores" some studies, e.g. a Canadian study reporting benefits of helmets.[4] In fact, the Canadian study illustrates why the criterion is necessary. The non-enforced law in Ontario increased %HW temporarily, with a return to pre-law levels by 1999 (Fig 2). If helmets were of significant benefit, percent head injury (%HI) should have responded to the increase in %HW, then returned to pre-law %HI with the fall to pre-law %HW. This did not happen; %HI continued to decline in over the entire period (1994-2002) implying that the original study (which considered data for 1994-98 only) was incorrect.
Mistakes such as the above reinforce the argument that helmet laws should be evaluated by considering only datasets that enable the response to changes in %HW to be separated from trends. Naive approaches simply reporting trends as effects of helmet laws (as in the Canadian study) would lead to the conclusion that bike helmet laws also prevent pedestrian injuries (Fig 3)! A more plausible explanation is that helmet-law provinces also introduced other measures (e.g. speed cameras or random breath tests) and that they improved safety for all road users.
It is a pity that Ms Thompson cites only the original Canadian study and ignores the more recent data I cited in Table B , showing that the original conclusions were false. The other studies she cites also failed to consider trends, or reported a non-significant effect of helmets when trends were included in the model.
Enforced helmet laws can produce extremely large effects. For example the decline in numbers of head and non-head injuries following Victoria’s helmet law suggest that the most obvious outcome was a reduction in cycle use. Greater effort is required to evaluate negative consequences of helmet laws, and compare the costs of reduced cycling, reduced safety in numbers and increased risk taking with benefits that are usually too small to be distinguishable from trends. The cost-benefits of helmet laws should also be compared with other measures to improve road safety, such as increased use of speed cameras or random breath testing. A peer-reviewed paper published in 2007 discusses these ideas in more detail.[5] By considering all aspects of helmet laws in conjunction with other methods of improving cyclist safety, the most cost-effective and beneficial measures will be implemented, allowing this healthy and environmentally friendly activity to be as safe and enjoyable as possible.
References
[1] Daniel R Hicks. Some observations from the US. BMJ Rapid Response, 26 July 2006. http://www.bmj.com/cgi/eletters/332/7543/722-a#138382
[2] Pucher J, Dijkstra L. Promoting Safe Walking and Cycling to Improve Public Health: Lessons From The Netherlands and Germany. Am J Public Health 2003;93:1509–1516.
[3] Kraus JF, Fife D, Conroy C. Incidence, severity, and outcomes of brain injuries involving bicycles. Am J Public Health 1987;77(1):76-8.
[4] Diane Thompson. Re: Objective observation of helmet use is essential. BMJ Rapid Response, 8 July 2006. http://www.bmj.com/cgi/eletters/332/7543/722-a#137351
[5] Robinson, D.L. Bicycle helmet legislation: Can we reach a consensus? Accident Analysis and Prevention 2007; 39:86–93
Competing interests:
None declared
Competing interests: No competing interests
In reply to James Redfield letter 7 June, relating to neck injuries
and helmet use resulting in a higher accident rate, there is reasonable
evidence to show helmet use results in more accidents for a number of
reasons plus more head/helmet impacts . In my letter 1st April , I try
to explain how helmet use can increase the accident rate due to additional
forces to the head at a time when maintaining balance may already be very
difficult. James Redfield believes it is irresponsible to raise these
issues but I would suggest it is essential in understanding helmet
effects.
My claim that helmet use can increase neck injuries is supported by
the executive summary of Attwell. Referring to the odds ratio stated
"Three studies provided neck injury results that were unfavourable to
helmets with a summary estimate of 1.36(1.00, 1.86), but this result may
not be applicable to the lighter helmets currently in use". I think the
bending moments to the neck could be more significant with the variation
in helmet weight as a secondary factor.
Reported cases of cyclists receiving major injuries due to high-risk
cycling accidents have appeared in the press and long term disabilities
may be the result of cyclists taking too many risks due to thinking they
are protected by wearing a helmet. One such example was reported in the
New York Times . In August 1999, Philip Dunham, then 15, was riding his
mountain bike in the Great Smoky Mountains National Park in North Carolina
and went over a jump on a trail. As he did, his back tire kicked up, the
bike flipped over and he landed on his head. The helmet he was wearing did
not protect his neck and he was paralysed from the neck down. Two years
later, Philip has regained enough movement and strength in his arms to use
a manual wheelchair. He has also gained some perspective. With the helmet
he felt protected enough to ride off-road on a challenging trail. In
hindsight, perhaps too safe. "It didn't cross my mind that this could
happen," said Philip, now 17. "I definitely felt safe. I wouldn't do
something like that without a helmet."
Fatality data does indicate a small proportion of cyclists deaths
involve serious neck injuries. From the above it appears neck injuries to
cyclists are a small proportion of overall injuries and helmet use
increases neck injuries.
Dr Robinson examined data on 10,479 head injuries severe enough to
appear in hospital admissions databases. The lack of obvious response in
head injury rates to increases of more than 40 percentage points in helmet
wearing shows that helmet laws have no benefit and many obvious drawbacks.
Just as Robinson found no benefit from helmet laws, studies of the
circumstances leading to cycling fatalities show that helmets are in fact
unlikely to save many lives. In Auckland, New Zealand, 16 of 19 non-
helmeted cyclists died from multiple injuries, so helmets would not have
changed the outcome. All these deaths resulted from collisions with motor
vehicles. Only one cyclist died from head injuries alone from a moderate
speed bike-only crash - that cyclist actually wore a helmet.
In Brisbane, Australia, an investigation of serious head injuries
reported that all deaths were caused by bike/motor vehicle collisions. For
13 of the 14 non-helmeted cyclists who died, there was no indication
that a helmet would have made any difference. The researchers were
very concerned about brain damage from rotational injuries and recommended
developing a test to measure sliding impact friction of helmets . This is
being investigated by the DfT.
Rotational injuries from sports helmets are a recognised problem:
"The use of helmets increases the size and mass of the head. This may
result in an increase in brain injury by a number of mechanisms. Blows
that would have been glancing become more solid and thus transmit
increased rotational force to the brain. These forces result in shearing
stresses on neurones which may result in concussion and other forms of
brain injury." Experiments on monkeys show that rotational forces cause
much more severe brain injuries than linear forces. One helmet designer,
concerned about serious brain damage from rotational injuries suffered by
motorcyclists, designed a new helmet to help combat the
problem. It has a polyethylene skin that moves independently of the inner
cushion (see http://www.phillipshelmets.co.uk/).
Mr Redfield also asks about the agenda, how best to resolve all these
issues, the real agenda, is one question I am trying to answer.
Competing interests:
None declared
Competing interests: No competing interests
A couple of observations, not directly addressing the controversy at
hand, but maybe giving some perspective:
First, as an Assistant Scoutmaster for a US Boy Scout troop, I
participated in some organized bike rides by Scouts. Scout rules require
helmet use, which is a good thing, since on these rides two Scouts
suffered serious falls.
In the first instance the boy ran off a trail at high speed and head-
on into a large boulder. He was thrown over the handlebars and landed
head-first on the boulder. In the second instance a mechanical failure on
the bike (front wheel was inadequately secured) caused the boy to again be
thrown over the handlebars, onto a railroad track.
In both cases the helmets were severely damaged, but the boys got
away with only scrapes and bruises. While I did not personally witness
either accident, from the condition of the helmets it's hard to believe
that significant head injury would not have occurred if the helmets had
not been worn.
It should be noted that these accidents are fairly typical of cycling
accidents in the US. Statistics show that most accidents involve running
into a stationary object or another cyclist or pedestrian, while only a
small minority involve a motor vehicle.
On the other (and my second point), several major cycling
organizations in the US have considered whether or not to support
manditory helmet legislation. Upon running through the available
statistics, however, they've concluded that that the health benefits of
cycling outweight (in an actuarial sense) the risks of riding without a
helmet (though they all believe that it is better still to wear a helmet).
For this reason they have generally not supported manditory helmet
legislation.
Competing interests:
None declared
Competing interests: No competing interests
Diane Thompson replying to Richard Keatinge (8 July) says "Your claim
that there is differential reporting of helmet use by head injured (cases)
and non head injured (controls) cyclists in published case-control studies
is mere speculation." This seems rather surprising because Rivara et al.
stated "one study that compared observations of helmet use to a statewide
telephone survey found that the survey overestimated helmet use by 15 to
20 percentage points".[1] Thompson’s comment that "There is good evidence
that self-reported helmet use is accurate" seems to be at odds with a
paper she co-authored.
As Dr Keatinge pointed out, potential biases in estimates of helmet
wearing are important because the benefits Ms Thompson and colleagues
claim for helmets depend on the validity of comparing helmet wearing of
head injured cyclists treated at emergency departments with a community
control group who fell off their bikes. Because of the difficulty finding
adults who crashed or fell off their bikes, 86% of the community controls
(CC) were children under 15.[2] At the time, a large observational survey
in Seattle showed that 3.2% of child cyclists wore helmets, compared to
21.1% of children in the CC group.[3]
If, as Ms Thompson suggests, these helmet wearing rates are correct,
it would seem that helmeted children fall off their bikes 7 times more
often than non-wearers. There would be no point in recommending helmet
wearing, because helmet wearers seem to have many more injuries than
non-wearers.
Why should helmet wearers have more accidents? Clarke details how
helmet use can lead to more head impacts plus additional accidents.[4]
Thompson's approach to helmet research appears to assume that differences
in head injury rates were due to helmets. This may appear reasonable, but
in practice there are many complications to consider.
For example, from 1988-1992, head injuries of vehicle occupants, motor
cyclists and pedestrians fell by 56% in South Australia.[5] If head injury
rates can change by such an extent over a 4-year period because people
take greater care and do not speed or drink drive, is it not possible that
the head injury rate for cyclists can also change
substantially without any effect of helmets? The injury rate for cyclists
varies from country to country and with the type of cyclist. The head
injury rate is also a function of the ratio of head injury to other
injuries and there is evidence that helmet use tends to increase the
overall accident rate, effectively changing the head injury rate.
A major problem with case-control studies is that they have no means
of measuring the overall accident rate. If subjects were assessed on how
much cycling they do, we could calculate head and other injury rates per
unit time, a much better approach than just considering numbers or
proportion of head injuries. It is time to move forward with helmet
research and consider the effect on balance and riding stability, as well
as looking at the best ways to reduce accidents, promote cycling and allow
for personal choice.
1 Rivara FP, Thompson DC, Patterson MQ, Thompson RS, Prevention of
bicycle-related injuries: Helmets, Education, and Legislation, Annu Rev
Public Health, 1998. 19:293-318.
2. Thompson, R. S., F. P. Rivara, et al. A case-control study of the
effectiveness of bicycle safety helmets. N Engl J Med 320(21), 1361-7,
1989
3. DiGuisseppi, C. G., F. P. Rivara, et al. Bicycle helmet use by
children. Evaluation of a community-wide helmet campaign. JAMA 262, 2256-
61, 1989.
4 Clarke CF, The Case Against Bicycle Helmets and Legislation, World
Transport Policy & Practice Volume 12 No. 3. 2006
http://www.ecoplan.org/wtpp/wtj_index.htm
5 North B, Oatey P, Jones N, Simpson D, Head injuries from road
accidents - a diminishing problem?, Med J Aust, Vol 158 March 15, 1993.
Competing interests:
None declared
Competing interests: No competing interests
July 2006
The Editor, BMJ
Dear Sir,
With due respect the letter “Re: Objective observation of
helmet use is essential” from Diane and Robert S. Thompson, BMJ
Rapid Responses, July 8, is misleading at best and it must be asked, to turn
their own question around, “Are you really trying to pursue the science
assessing cycle helmet efficacy and population effectiveness or is this some
sort of crusade on your part to fit the science to your beliefs?”
Drs Thompson dismiss Robinson [d] as the studies reported
there are not primarily case-controlled ones, and suggest Robinson simply
ignores studies with which she does not agree. The New Zealand
Government’s compulsory experiment has undergone a cohort review
[b], which is less liable to selection bias and therefore stronger than a case-
control study [c]. Yet Drs Thompson and Hagel et al [i] appear to simply
dismiss it — does it not fit their beliefs?
In New Zealand a whole population of some 4 million people
have been either compelled to wear helmets while riding a bicycle or told not
to bicycle – despite health indications to the contrary the New
Zealand political message has solidly been that not bicycling is better than
doing so sans plastic hat. The population wide data in New Zealand should
show something like the often claimed, and just as often challenged, 85%
reduction in head injuries to bicyclists. It simply does not. This has been
reported in an earlier letter [a] in response to Hagel et al [i], that was based
on previous published data by Perry [b], and a similar analysis is also
provided by Robinson [d].
While some studies, particularly pre-legislation, have shown
some small benefits; other, later studies, have shown total failure. Benefit
cost studies have shown the costs swamping meagre benefits. It might be
nice if the helmet legislation had worked, but wishful thinking is not science
and doesn’t prevent injuries or improve health. Narrow case-
controlled studies seem to miss this big picture — across a whole
population the measure did not work.
New Zealand's problem is unfortunately that the experiment
was enforced by law, and political expedience doesn't allow the easy removal
of laws, even failed ones. Government policy is now to increase cycling, in
light of growing health issues such as child obesity, and they are battling
some twenty years of telling people the activity is extremely dangerous
— those charged with implementing this policy have publicly admitted
they created a problem for themselves.
The closing comments of Drs Thompson show how
unscientific the approach is. With due respect it might be easier simply to re-
word them slightly: “We predict [a review of research] will lead you to
the conclusion that we have reached, that kevlar vests prevent gunshot
injuries and increased wearing rates result in decreased gunshot injuries to
people”. Do people call for population-wide compulsory kevlar vests?
Of course not.
Those who oppose bicycle helmet legislation do not claim that
these plastic hats cannot prevent some injuries, to do so would be
unsupportable. Rather they oppose the legislation because it does not work
across a population to decrease injuries and increase health [b, d]. By
suggesting that those who oppose their view do so for a reason they do not,
Drs Thompson are being misleading at best.
What is revealing is how those who expound the plastic hat
wearing theory, namely that they are so effective at reducing head injuries
that to not do so is unwise at best, actually practice their own theory. It has
long been known that the theory does not only apply to those on bicycles,
those involved in anything from walking to driving have at times been
extolled, or forced, to wear “bicycle style” plastic hats.
Back in 1997 the Australian Government published research
claiming that if seat-belted, airbag-protected, car occupants wore bicycle-
style helmets a saving of A$380M/year would accrue from reduce head
injuries, rising to A$500M/year without airbags [g]. Since then they have
continued to pursue research in this area [h].
In 2003 the New Zealand Minister of Transport wrote that the
Government “does not dispute that helmet wearing could reduce the
severity of head injury for car occupants in crashes. However, given the
currently extremely low level of helmet wearing by car occupants, the
introduction and enforcement of mandatory helmet wearing would be
impracticable.” [f]
Ignoring that the NZ Government had supported a decade long
campaign to persuade bicyclists to wear helmets so that legislation would
become practicable, we need to ask why is there such a low level of helmet
wearing in cars given the claims by Drs Thompson that those driven by
science and not belief support the plastic hat theory? Where are all those
scientists in cars wearing helmets? They do exist; for example Dr Jack
McClean, director of the National Health and Medical Research
Council’s road accident research unit in Adelaide has happily been
photographed with helmet on in the car [e]; but they remain the exception
rather than the rule.
“You should wear a helmet, and the law should compel
you to do so, but we choose not to ourselves even when our theory says we
should.” Science or something else?
Selected case-control studies, the ignoring of trends, and the
dismissal of population wide failures. With all due respect, is this really
science?
Let us not forget that during the 3rd International Conference
on Injury Prevention and Control, Melbourne 1995, that delegates from
Sweden stated, tearfully, that their helmet promotion activities had result in
deaths. The Drs Thompson where present I believe. The response to this
tragedy was to develop a helmet that fell off on impact. Science or belief?
It is clear that were the NZ Legislature driven by science and
not political expedience the health, safety & financial disaster that is the
NZ Bicycle Helmet legislation would long have been abandoned. The British
medical profession should be taking note of this and act to ensure that a
similar disaster is not visited upon the British by the “Martlew
Bill” or anything else.
Yours,
N
Perry, Scientist & Mathematician, New Zealand
[a] Perry, N. Letter to BMJ, March 2006, available at http://kaka.research.zoot.net/bmj/march_letter.html
[b] Perry, N., The Bicycle Helmet Legislation, Curse or
Cure?, Cycling 2001, Christchurch.
[c] For example, see the hierarchy of evidence in
“Systematic reviews: what are they and why are they useful?” at http://www.shef.ac.uk/scharr/ir/units/systrev/
hierarchy.htm
[d] Robinson, D. L., No clear evidence from countries
that have enforced the wearing of helmets, BMJ 2006;332:722-725
[e] Innes, Stuart, A new head start for car safety,
Adelaide Advertiser, 20 May 1993
[f] Hon Paul Swain, Minister of Transport, New Zealand,
Letter To: Hon Peter Dunne, Leader, United Future, 28 May
2003
[g] McClean, A. J, et al, Prevention of Head Injuries to
Car Occupants, Federal Office of Road Safety, CR 160, ISBN 0 642
51349 X, 1997
[h] Anderson, R., et al, Further Development of a
Protective Headband for Car Occupants, Australian Transport Safety
Bureau, CR 205, ISBN 0 642 25574 1, 2001
[i] Hagel, B., Macpherson, A., Rivara, F. P., Pless, B.,
Arguments against helmet legislation are flawed, BMJ
2006;332:725-726
Competing interests:
None declared
Competing interests: No competing interests
Reply to Keatinge “Objective observation of helmet use is essential”
(1) and two email communications to us on the same topic. Your questions
and/or statements are listed below with our responses.
YOUR STATEMENTS “Cyclists without head injuries will report rates of
helmet wearing much higher than their true rate. Cyclists with recent head
injuries, as in the case-control studies, will not be able to deceive
themselves or their interviewers, and will report much lower, truer rates
of helmet wearing. This bias is enough to account for all the positive
findings in case-control studies:” (1) AND “The promising results of the
case-control studies could trivially be accounted for by the hypothesis
that most cyclists exaggerate their helmet use, but head-injured ones do
not because after a demonstrable injury to the head they can’t fool
themselves in that particular way. (Robinson’s results do not rely on self
-reporting.)” 22 June email AND “in one case-control study based in
Seattle, 7% of the cyclists with head injuries reported wearing helmets,
as compared with 24% of the emergency room controls and 23% of community
cyclists who had had an accident(2) However, less than 6% of cyclists on
the Seattle streets at the time were actually observed to wear helmets (3)
Either helmets are a serious cause of accidents, or self-reports of helmet
use are not valid” (1)
OUR ANSWERS: Your claim that there is differential reporting of
helmet use by head injured (cases) and non head injured (controls)
cyclists in published case-control studies is mere speculation. There is
no evidence that controls, or for that matter cases, report helmet use
incorrectly. There is good evidence that self-reported helmet use is
accurate. Remember, all these cyclists had an injury that caused them to
seek medical care. This is an important event which people remember
accurately. Additionally, there were no helmet laws in Seattle at the
time. Observations of helmet use in the general cycling population after
helmet legislation (4) or before and after a helmet promotion campaign (3)
provide no information as to whether any of these cyclists were wearing
helmets when they crashed and went to the hospital. The studies of
observed helmet use in the work cited above provide information on the
prevalence of helmet use in the general cycling population. The case
control studies provide the prevalence of helmet use in cyclists who seek
ED treatment following a crash, a much different circumstance.
YOUR STATEMENT: “Robinson presents the best available evidence
derived from objective assessment of helmet wearing. Her demonstration
that cycle helmet laws do not work is likely to remain the definitive
answer.” (1)
OUR ANSWER: The studies that Dorothy Robinson cites in her recent
BMJ article (1) are time series studies or ecological designs which do not
have appropriate comparison groups. We have pointed this out in our
discussions with you, Dorothy Robinson, Bill Curnow and Mayer Hillman over
the past ten years. Please re-read our replies to your criticisms of our
Cochrane review. These are available at the end of the review (5) or on
the web at the following address: www.cochrane-
injuries.lshtm.ac.uk/helmetcomment.pdf Additionally, Robinson selects
portions of the studies which support her arguments and ignores the
portions which indicate a reduction in head injuries following
legislation. (6) She also omits 2 studies from North America which
indicate legislation reduces head or brain injury. (7,8)
YOUR QUESTION: “I would be interested to know how this data
collection was done in this study, and in particular how helmet use was
ascertained. Was it done by observation, by questionnaire in hospital, or
by later follow-up?" (Email of 29 May, 2006 to inquire about our Cycle
Helmet studies: NEJM, 1989 and JAMA, 1996.(2,9)
OUR ANSWER: In reply, both studies were prospective case control
studies so the data were collected in an ongoing fashion as the bicycle
crashes occurred and the riders sought treatment in the emergency
departments (ED’s) at the participating hospitals. Hospital ED’s were
visited at least once a week to identify bicycle riders who were injured.
Helmet use was determined by self-report using mailed questionnaires sent
to each identified cyclist following the ED visit. People who did not
respond promptly were interviewed by telephone using the same
questionnaire. Helmet use was ascertained from these completed
questionnaires.
YOUR STATEMENTS: “I would be interested in any information you can
give on the degree of independence of these two sources of data on helmet
wearing, and on any records of whether emergency room staff actually saw
the helmets themselves.” AND “The hypothesis that most cyclists exaggerate
their helmet use, but the head-injured ones do not because after a
demonstrable injury to the head they can’t fool themselves in that
particular way.” (22 June Email )
OUR ANSWER: We also abstracted the medical record of those cyclists
in the study and tabulated information about helmet use as recorded by ED
personnel. The medical record was written when the patient was treated in
the ED. This ascertainment is independent of helmet use reported
subsequently on the research questionnaire. This permitted independent
corroboration of reported helmet use. We compared the report of helmet use
in the medical record to the report of helmet use on the questionnaire and
assessed the agreement between the ED record and the questionnaire report
of helmet use. Agreement was almost 100% for both cases and controls. (9)
In many cases the attending physician or emergency staff saw the
helmets.
In addition, independent laboratory analysis of 500 of the helmets
which were damaged in the crashes indicated that cyclists reported helmet
type correctly. This is a more complex memory task then reporting whether
a helmet was worn. (10) In conclusion, the multiple methods used to
ascertain helmet use provide solid evidence for the validity of self
reported helmet use.
SUMMARY : The question here for you and other doubters at this point
is; Are you really trying to pursue the science assessing cycle helmet
efficacy and population effectiveness or is this some sort of crusade on
your part to fit the science to your beliefs? Over the years my colleagues
and I have explained case control studies and other epidemiologic methods
of conducting studies and analyzing statistics. (See our Cochrane review,
our comments replying to numerous criticisms, Peter Cummings’ recent
article in Accident Analysis and Prevention,” Misconceptions regarding
case-control studies of bicycle helmets and head injury”.(5,11) You could
also read the article by Brent Hagel et al “Arguments against helmet
legislation are flawed” which is published the same March issue of BMJ as
Dorothy Robinson’s article. The rapid responses from anti-helmet writers
are simply offering the same old arguments, opinions and speculations that
have been written by the same people for years. If you truly wish to move
the science forward in this area, we respectfully request that you all
take some formal courses in the use of Epidemiological methods, non-
experimental design and biostatistics. After that you should review the
whole body of peer-reviewed published information with an open mind and
see where your review leads you. We predict it will lead you to the
conclusion that we have reached, that cycle helmets prevent head and brain
injuries and increased wearing rates result in decreased head and brain
injuries in cyclists. (5,6)
References
1. Keatinge,RM. Objective observation of helmet use is essential. BMJ 14
May 2006.
2. Thompson RS, Rivara FP,Thompson DC. A case-control study of the
effectiveness of bicycle safety helmets. NEJM 1989;320:1361-7.
3. DiGuiseppi CG, Rivara FP, Koepsell T, Polissar L. Bicycle helmet
use by children. Evaluation of a community-wide helmet campaign JAMA
1989;262:2256-2261.
4. Robinson DL. No clear evidence from countries that have enforced
the wearing of helmets. BMJ 2006;332:722-5.
5. Thompson DC, Rivara FP, Thompson RS. Helmets for preventing head
and facial injuries in bicyclists. Cochrane Database Syst Rev 2000;(2):
CD001855.
6. Hagel B, Macpherson A, Rivara FP, Pless B. Arguments against
helmet legislation are flawed. BMJ 2006:332:725-6.
7. Lee BH, Schofer JL, Koppelman FS. Bicycle safety helmet
legislation and bicycle-related non-fatal injuries in California. Accid
Anal Prev 2005;37:93-102
8. Macpherson AK, To TM, Macarthur C, Chipman ML, Wright JG, Parkin
PC. Impact of mandatory helmet legislation on bicycle-related head
injuries in children: a population-based study. Pediatrics 2002;110:e60.
9. Thompson DC, Rivara FP, Thompson RS. Effectiveness of bicycle
safety helmets in preventing head injuries: A case-control study. JAMA
1996;276:1968-1973.
10. Ching RP, Thompson DC, Thompson RS, Thomas DJ, Chilcott WC,
Rivara FP. Acc Anal Prev 1997;29:555-562.
11. Cummings P, Rivara FP, Thompson DC, Thompson RS. Misconceptions
regarding case-control studies of bicycle helmets and head injury. Accid
Anal Prev 2006;38:636-643.
Competing interests:
None declared
Competing interests: No competing interests
For Mr. Clarke to continue to push the idea that bicycle helmets
somehow
cause bicycle crashes is completely irresponsible. Mr. Clarke cites a 1988
report (1), an unpublished Current Affair bulletin (2) that is not widely
available but apparently from Australia, and his own web pages (3) to
support his irresponsible argument.
On his 2003 web page, after much questionable data analysis, Mr.
Clarke
concludes that "Neck injuries also increase because of HELMET WEARING AND
CAN LEAD TO DEATH OR SEVERE INJURIES INCLUDING PARALYSIS." [emphasis
added] There is simply no credible evidence to support this absurd claim.
It seems Mr. Clarke has a clear hidden agenda. He does not like
helmets when
riding a bicycle. That is fine for him. But to continue to try to
perpetuate his
discredited myths is dangerous, especially to the most at risk group,
young
boys 10-15 years old.
1 Wasserman RC; Bicyclists, Helmets and Head Injuries: A Rider-Based
Study
of Helmet Use and Effectiveness; AJPH Vol 78, No 9, pp 1220-21, September
1988.
2 Curnow WJ; Road Rules OK? Self protection and social damage;
Current
Affairs Bulletine Australia, April/ May 1998.
3 Clarke CF, Bicycle helmets and accident involvement; Cycling World,
UK,
June 2003 – see: http://www.cycle-helmets.com/cyclingworld.htm
Competing interests:
None declared
Competing interests: No competing interests
James Redfield might want to reexamine some of the presumed facts
(attributed to an unsourced 2000 CDC report) cited in his letter of 18
May:
* While it's true that ~813 bicyclists were killed in collisions with
motor vehicles in 1997, the idea that 97% were not wearing helmets is
simply an artifact of how the National Highway Traffic Safety
Administration’s Fatality Analysis Reporting System (FARS) failed to
accurately record bicycle helmet use back then.
At the time, most police accident reports did not indicate whether a
helmet was worn. Instead of listing helmet use as “unknown”, FARS
erroneously coded nearly all of these cases as "helmet not used”. This is
borne out by a comparison of FARS data with equivalent state data where
some effort was actually made to determine helmet use status—e.g.
California’s Statewide Integrated Traffic Record System (SWITRS) and
Florida’s Department of Highway Safety and Motor Vehicles (DHSMV), which
together account for over 30% of all bicycle-related fatalities in the US.
From 1997-2000, more than 16% of fatally injured CA bicyclists were
determined to have been using a helmet according to SWITRS [1], but only
2.5% of those same CA bicyclists were supposedly doing so according to
FARS [2]; and even SWITRS considerably underestimates total helmet use
since it explicitly states that all “helmet use unknown” cases are counted
in with the “helmet not used” cases instead of being treated separately.
Similarly in Florida, from 1994-98 6.5% of fatally injured bicyclists were
determined to have been using a helmet according to DHSMV [3], but less
than 0.2% (i.e. just 1 out of nearly 600) according to FARS [2].
Though the undercounting of bicycle helmet use in FARS has lessened
considerably in recent years (for 2004 FARS indicates that 90 of 725
(12.4%) fatally injured bicyclists had definitely been wearing a helmet,
with another 32 (4.4%) listed as unknown helmet use [2]), it's fairly
clear that FARS continues to significantly undercount actual helmet use.
* The only way to get anywhere close to the claim that ~140,000
children are treated for head injuries each year as a result of bicycling,
is by defining “children” as anyone under the age of at least 21 and by
counting all injuries to the ears, eyes, mouth, and face (which most
bicycle helmets are clearly not designed to protect against), along with
scalp lacerations, skull fractures, concussions, and other traumatic brain
injuries that have traditionally been defined as head injuries.
According to the US Consumer Product Safety Commission’s National
Electronic Injury Surveillance System (NEISS), the total number of actual
head injuries to bicyclists under the age of 16 is generally estimated to
be on the order of 40,000-50,000 per year, and of that number just 3000-
4000 are serious enough to result in hospitalization--though even these
most serious of head injuries have declined to well under 3000 per year in
recent years [4].
* Likewise, claiming the 1991 “societal costs associated with bicycle
-related head injury or death were estimated to exceed $3 billion” is
highly dubious. Comparing NEISS data [4] with what the CDC actually has
to say about traumatic brain injury (TBI) [5], we find that bicycling
accounts for <5% of the 1.4 million people who sustain any kind of TBI
in the US, <3% of the 235,000 hospitalized for a TBI, and just 1% of
the 50,000 who die from a TBI each year. It is therefore unlikely that
bicycling represents more than 5% of the total direct and indirect costs
of TBI, estimated by the CDC to be $60 billion/year in 2000 [5].
More important for a discussion on helmet laws, the relevant issue is
not the total cost of TBI, but the change in injury costs from legislation
compared to other costs, such as reduced cycling because of legislation.
While "confounding" is one possible explanation why helmet laws have not
been observed to be effective in reducing serious head injuries or
fatalities, over and above that due to reduced cycling from the imposition
of such laws, those with a more open mind might wish to consider some
alternative hypothesis (e.g. risk compensation) that might better explain
the lack of supporting statistics.
It is also worth noting that while the CDC still appears to accept
the highly controversial contention that bicycle helmets could prevent 85%
or more of “serious” head injuries, they have at least scaled back on
their earlier absurd claim that ~500 bicycle fatalities could somehow be
avoided each year with universal helmet use [6], and now only assert ~150
lives per year would be saved [7]—though there is of course no real-world,
whole-population data to support even this more modest claim either.
Indeed, those who prefer to put their trust in empirically derived
evidence might well conclude there is no valid basis for the imposition of
mandatory helmet laws on otherwise unoffending cyclists, and that even
aggressively promoting increased voluntary helmet use might not
necessarily be a good idea if based primarily on the type of dangerously
deceptive data that distorts the actual risks of cycling and/or
dramatically oversells the limited protective benefits helmets may
actually have to offer.
[1] http://www.chp.ca.gov/switrs/
[2] http://www-fars.nhtsa.dot.gov/queryReport.cfm?stateid=0&year=2004
[3] http://www.hsmv.state.fl.us/reports/crash_facts.html
[4] http://www.cpsc.gov/library/neiss.html
[5] http://www.cdc.gov/ncipc/tbi/TBI.htm
[6] http://wonder.cdc.gov/wonder/prevguid/m0036941/m0036941.asp
[7]
http://www.cdc.gov/ncipc/fact_book/11_Bicycle_Related_Injuries.htm
Competing interests:
None declared
Competing interests: No competing interests
Dr Redfield letter 18 May states, Dr. Keatinge is wrong to state that
"excess accidents caused by helmets remain an additional possibility"
without any corroborating statistics. In actual fact there is evidence to
support Dr Keatinge's claim. One report detailed interviewing 516 cyclists
in a roadside survey, including 40 wearing helmets (Wasserman 1). Out of
21 reported falling and hitting their heads, 8 were helmeted and 13 were
non-helmeted. The accident rate for helmeted would be 20% of their group,
8 from 40, and non-helmeted 2.8% of their group, 13 from 476, indicating
non-helmeted had fewer accidents. Another article detailed an increased
risk to cyclists aged under 16 years in New South Wales following
legislation when "other injuries" proportionately increased by 68% (Curnow
2). One report provides several examples of helmet use being associated
with an increased accident rate, Clarke 3. Dr Keatinge is correct to
reflect the available evidence.
Dr Redfield quotes from the American CDC, regarding bicycling in the
USA where over 70 million people are estimated to cycle. Some of the CDC
so called facts may not actually be correct. I noticed one estimate they
quoted, 13/12/98, stating "It is estimated that 75% of bicycle-related
fatalities among children could be prevented if all children wore
helmets". In contrast to such a claim, the National Children's Bureau4
state from 18 deaths to child cyclists aged 0-15 in GB in 2003, only 3
could be expected to be prevented by wearing helmets. In practice the NCB
may have overestimated the benefits of helmets because they did not
consider how helmets incur more impacts due to being larger than the bare
head and they could have been misled by how some information has been
presented.
It appears the medical profession could be much better and more
reliably informed and I feel sure the CTC, the UK's national cycling body,
could assist the BMA with this matter.
1 Wasserman RC; Bicyclists, Helmets and Head Injuries: A Rider-Based
Study of Helmet Use and Effectiveness; AJPH Vol 78, No 9, pp 1220-21,
September 1988.
2 Curnow WJ; Road Rules OK? Self protection and social damage;
Current Affairs Bulletine Australia, April/ May 1998.
3 Clarke CF, Bicycle helmets and accident involvement; Cycling
World, UK, June 2003 – see: http://www.cycle-helmets.com/cyclingworld.htm
.
4 Gill T, 'Cycling and Children and Young People' refer web site
www.ncb.org.uk
Competing interests:
None declared
Competing interests: No competing interests
Not absurd, logical
The contention is not absurd. It may be true, or untrue, or the
situation arise through unknown perturbing factors (whcih would be more
interesting than those we know already and worth looking for).
It might be statistically incorrect, although I do not see in what
way.
But it is not absurd, it is a clearly set out logical deduction from
a set of figures which appear to be taken as correct by the arguer from
absurdity.
Which is.
Competing interests: No competing interests