No clear evidence from countries that have enforced the wearing of helmets

BMJ 2006; 332 doi: http://dx.doi.org/10.1136/bmj.332.7543.722-a (Published 23 March 2006)
Cite this as: BMJ 2006;332:722.2

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25 October 2010

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: None declared

Adrian K Midgley, GP

Exeter EX1 2QS

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14 January 2007

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: None declared

Dr Dorothy L Robinson, Consultant Statistician

Armidale

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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: None declared

Colin F Clarke, Hon Secretary CTC Yorkshire and Humber Region

York YO41 1BU

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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: None declared

Daniel R Hicks, Programmer

Rochester MN 55901 USA

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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: None declared

Nigel Perry, Scientist

New Zealand

Christchurch

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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: None declared

Colin F Clarke, Hon Sec CTC Yorkshire and Humber Region

York YO41 1BU

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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: None declared

Diane Thompson, Epidemiologist (retired)

Robert S. Thompson

Harborview Injury Prevention & Research Center, Univ of Washington, Seattle, WA 98104 USA

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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: None declared

James A. Redfield, Medical Information Systems Developer

95054

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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: None declared

Riley R Geary, traffic safety analyst

Institute for Traffic Safety Analysis, Arlington, VA 22204

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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: None declared

Colin F Clarke, Hon Sec CTC Yorkshire and Humber Region

YO41 1BU

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