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PAPERS: Adrian Cook and Aziz Sheikh Trends in serious head injuries among cyclists in England: analysis of routinely collected data BMJ 2000; 321: 1055 [Full text]

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Alternative explanation for the trend in head injuries

Conor Linstead   (28 October 2000)

more helmet nonsense

Douglas Salmon   (28 October 2000)

Inadequate Control for Confounding Factors

Avery Burdett   (29 October 2000)

Helmets? Make drivers wear them.

Colin Guthrie   (30 October 2000)

Perception over reality

Piers Simey   (30 October 2000)

Re: Helmets? Make drivers wear them.

Aedan McGhie   (31 October 2000)

A BALANCE OF RISKS

William Sellwood   (31 October 2000)

A Lack of Respect

Tony Whiffen   (31 October 2000)

Re: A BALANCE OF RISKS-dont fall off

G H Hall   (1 November 2000)

Why focus on helmets?

Glenn Stewart   (1 November 2000)

Protection difficult to prove

Mike Clark   (2 November 2000)

A failed analysis

Richard Keatinge   (6 November 2000)

Head injuries in cyclists

Stephen Butterworth   (7 November 2000)

Curate's egg

Simon Baddeley   (11 November 2000)

Bicycle helmets again!

Anthony Campbell   (13 November 2000)

Dangers of Cycling

Lee Jeys   (21 November 2000)

Re: Dangers of Cycling

Ian Nesbitt   (22 November 2000)

Cycle helmets

Mayer Hillman   (30 November 2000)

scottish data shows fall in head injury

Adam Redpath   (21 December 2000)

Alternative explanation for the trend in head injuries 28 October 2000
Conor Linstead, Researcher London Send response to journal: Re: Alternative explanation for the trend in head injuries	From the data presented by Cook and Sheik, it cannot be inferred that the reduction in head injuries over the study period relative to the total number of cyclist injuries indicates a correlation between wearing cycle helmets and a reduced incidence of head injuries. The data are insufficient to draw this conclusion. The authors have failed to account for confounding factors that influence the types of accidents involving cyclists, such as traffic patterns and cycle facilities. The author’s hypothesis may indeed be correct but the same trend could potentially result from other scenarios. For example, the period of the study coincides with an increased awareness of cycling issues amongst local authorities and an associated increase in the provision of cycle facilities such as advanced stop lines and cycle lanes and paths. It is quite feasible that these facilities lead to a reduction in the type of accidents that result in head injuries while increasing the number of more minor accidents, giving a constant rate of admission but a reduction in head injuries. In my opinion the biased interpretation of the data in this paper adds little to the debate on the effectiveness of cycle helmets.
more helmet nonsense 28 October 2000
Douglas Salmon, GP Partner birmingham Send response to journal: Re: more helmet nonsense	True, helmet wearing might make a small difference to the rate of head injuries in cyclists. However a cyclist in the UK is 6 times more likely to be killed than in Denmark or Holland, where virtually nobody wears helmets. The problem is not abscence of helmets, but abscence of a culture of respect for cyclists evident amongst both motorists and planners. This sort of research is about blaming victims rather than solving problems.
Inadequate Control for Confounding Factors 29 October 2000
Avery Burdett, Researcher, cycling accidents n/a Send response to journal: Re: Inadequate Control for Confounding Factors	The authors refer to lack of controls in other studies but it appears their own study lacked a few of its own. Most but not all serious head injuries to cyclists result from motor vehicle involvement. The authors appear not to be aware of, and the report does not acknowledge, an important change in the pattern of cycling that may mask a change in motor vehicle involvement. With the trend of a rising popularity of the mountain bike has come an increase in off-road trail cycling. Thus, while overall cyclist exposure to the risk of an accident may have remained constant, the exposure to risk of an accident involving a motor vehicle may have fallen. Another serious omission is the absence of information on prevailing rates of head injury among other road users. Robinson in Australian Doctor, 27 February, 1998, http://lash.une.edu.au/~drobinso/ozdoc.html showed cyclists in Western Australia over a two decade period experienced declining head injury percentages similar to other road users, substantially because of a series of driver behaviour modification measures imposed by the government. More of Robinson's research on the effects of Australian bicycle helmet legislation can be found at: http://lash.une.edu.au/~drobinso/velo1/velo.html Additional sources are on The Bicycle Helmet FAQ at: http://www.magma.ca/~ocbc
Helmets? Make drivers wear them. 30 October 2000
Colin Guthrie, General Practitioner 1448 Dumbarton Road Glasgow G14 9DW Send response to journal: Re: Helmets? Make drivers wear them.	Why are helmets not compulsory for drivers of motor vehicles? I believe that cyclists would be at far less risk if seat belts were illegal and every car had a dagger placed strategically at the centre of the steering wheel and pointing at the driver's chest. When you are being bombed you don't hide in air raid shelters, you stop the bombing. Here's a cycling rap for you all...now put plenty of whooomph into the YAH...HOOO bit! Yah..HOO The time is right. I’m on the bike , I’m moving well I’m really in charge, the cars can tell These days in the saddle are such a treat I’m buzzing from my head to the tips of my feet Yah ---Hooo ! The energy's flowing It feels so good, don’t care where I’m going Yah---- Hoo ! Get outta my way! Now just you listen to what I have to say The time has come , the time is right It’s time for us to stand and fight Our streets destroyed , so many taken It’s time for us to really shake 'em Yah---Hoo! C’mon and shout It’s time to get the heavy metal out Yah—hoo! We must be free From all this vile machinery Nought to sixty, it makes me sick Why does ‘size matter’ to a driver's dick? If you buy a Peugeot, watch your back Your woman can expect a shark attack? Yah—hoo! Car culture crap! A culture that we need to scrap Yah—hoo! We should be free From all this vehicular insanity. Keep on cycling..without it you're dead.... helmets would really..... 'knock it on the head.' Let the red lights roll! Yah...Hooo! Colin Guthrie (aka Grey Triker)
Perception over reality 30 October 2000
Piers Simey, Physical Activity Adviser MSW Health Authority Send response to journal: Re: Perception over reality	As a physical activity adviser working within the NHS (and a London cyclist), this article highlights an important part of the debate on promoting cycling which should not be viewed in isolation. Awareness of declining trends in serious cycling injuries from helmet use may comfort some, but the perception of risk for the individual is crucial. Although wearing them should be encouraged, good quality helmets are not cheap and their use will not lessen the wobbles caused from being "buzzed" by passing cars. From a public health viewpoint, we should focus on providing accessible and affordable ways for sedentary people to become more active. It has been suggested that cycling at least 20 miles a week reduces the risk of heart disease to less than half that of people who are sedentary (Morris, 1989). The safe separation of cyclists and motor vehicles has also been highlighted by the Independent Inquiry into Inequalities in Health as a goal for reducing health inequalities (Acheson, 1998). Until there is significant investment in local cycle routes, the potential for cycling to impact on the prevalence of heart disease and inequalities in health would seem to be diluted. Morris, J. (1989) Proceedings of Cycling and the Healthy City. British Heart Foundation, London Acheson, D. (1998) Reducing Health Inequalities - A New Direction For Public Policy. London: The Stationary Office.
Re: Helmets? Make drivers wear them. 31 October 2000
Aedan McGhie, biology teacher Springburn, Glasgow Send response to journal: Re: Re: Helmets? Make drivers wear them.	4 years ago I was cycling to work and was hit by a car coming out of a side road. I of course leapt off the road and inspected my mount for damage. I then noticed blood pouring onto the road so I went to Monklands hospital to get stitched up. In the admissions area I was asked if I was wearing a helmet. It so happend that I was but only because it was February and polystyrene is decent insulation. I told them that yes, I had been wearing one but as I had landed on my chin it wasn't important. I told them this several times. Nonetheless, if stats were kept of this admission it will be recorded as one where a cyclist was hit by a car and survived while wearing a helmet. aedan
A BALANCE OF RISKS 31 October 2000
William Sellwood, Medical Student Glasgow University Send response to journal: Re: A BALANCE OF RISKS	In terms of evidence, I do not think that this paper alone proves very much about how helpful cycle helmets are at preventing death in cycle accidents. I believe that every effort should be made to encourage people to use their bicycles. Enforcing helmets will not encourage people to cycle, and I do not think it would be sensible plan of action. Perhaps a more useful question would be the following: By cycling is my risk of cardiovascular disease is lowered more than my risk of death by head injury is increased? I should add that I do wear a helmet myself because I feel safer with one!
A Lack of Respect 31 October 2000
Tony Whiffen, Civil servant Send response to journal: Re: A Lack of Respect	I concur with Douglas Salmon's comments above. As a cyclist I have been involved in a number of accidents with motor vehicles, and in none of these have I suffered head injuries or been wearing a cycle helmet. Instead, as cyclists tend to be slower, it would appear that some motorists think they can disregard their right of way, and pull out on cyclists simply to get ahead of them. It is this sort of attitude and the 'need for speed' or quickness, which needs to be tackled, not the need for cycle helmets.
Re: A BALANCE OF RISKS-dont fall off 1 November 2000
G H Hall, retired Send response to journal: Re: Re: A BALANCE OF RISKS-dont fall off	A lot depends on how reliable the evidence is that more people have been using helmets than before. The figures kindly provided by the authors show samples of about 250 children studied per year, with uncertain allocation to 6-10yr and 11-15 yr ages. It is not stated where the samples were obtained, or how. Without this information no conclusion about the reliability or validity of the conclusions is possible. The hospital records of helmet use or not would be highly desirable. Unfortunately we are still unable to make a clear recommendation. Following a basal skull fracture I sensibly wear a helmet under circumstances like those obtaining at the time of my accident- rough riding through a puddle of unknown depth. Is there a good database of information of this sort? Specific advice based on experience would be more acceptable than the "Thou shalt not" blanket nannying. GH Hall MD
Why focus on helmets? 1 November 2000
Glenn Stewart, Health Promotion Advisor West London Health Promotion Agency Send response to journal: Re: Why focus on helmets?	In Odense (Denmark) approximately 45% of 25 year olds cycle to work everyday and 70% do so in the summer. Almost no-one wears a helmet. Instead they have built a comprehensive system of segregated cycle lanes through which the whole population can undertake the levels of physical activity recommended for good health. Regardless of the debatable effects of helmets would it not be more useful to focus on changing the environment that makes people feel that they need to protect themselves whilst engaging in healthy behaviour?
Protection difficult to prove 2 November 2000
Mike Clark, Lecturer in Immunology Cambridge University Send response to journal: Re: Protection difficult to prove	The analysis by Cook and Sheikh unfortunately does not add any substantial strength to the case in favour of helmet use for reducing head injuries whilst cycling. Others in this thread have pointed out flaws in the analysis which allow other explanations for the results to be proposed. I am a regular cyclist and I do choose to wear a helmet. Also I am a rock-climber and again I choose to wear a helmet. Common sense seems to tell me that there will be a benefit from wearing a helmet which is why I do so. However as a scientist I think that studies should be very carefully designed so as not to give ambiguous results. A proper controlled study really needs to be done to take into account all confounding issues. Only then is it appropriate to lead with press releases indicating that the case for helmet use is proven. As an anecdote I do know of at least one colleague who survived a serious collision with a car in which her helmet was embeded in the radiator of the car, but in which she had only minor injuries. Another colleague who regularly wore a helmet whilst cycling was killed in an accident through sustaining head injuries on a rare occassion when she chose not to put in on. But these are anecdotes not hard evidence.
A failed analysis 6 November 2000
Richard Keatinge, GP trainee Wales Send response to journal: Re: A failed analysis	Sirs, The debate on bicycle helmets is particularly sad, because of the grotesquely inadequate data so repeatedly produced as decisive. Cook and Sheikh's paper1 is not the worst of a bad bunch, but neither does it provide useful support for the idea that cycle helmets could usefully improve the public health. They show from routine data a marginal decrease in the proportion of cyclists' hospital admissions that have head injuries as the primary diagnosis. As a clinician and epidemiologist I am aware of how powerfully diagnostic fashions can change over time, but this possibility cannot be addressed by their dataset and is ignored in the paper. They quote a personal communication in support of the idea that helmet wearing rates have increased over the same period, from 1991 to 1995. I am obliged to them for letting me have the data from this communication, which seems to be based on a questionnaire to less than 300 children. The most parsimonious inference from it is that, after years of "health promotion" bombardment, some schoolchildren have learned what answers to give to questionnaires. In any case, the simplistic supposition that helmets are responsible for the reduction is quantitatively absurd; among secondary schoolchildren the reduction of head injuries is given as 12%, while the increase in helmet wearing is only 10%. Do Cook and Sheikh really wish to suggest that helmets give protection even when they are not being worn? It is clearly ridiculous to suggest that Cook and Sheikh have demonstrated any causal relationship. Whatever the time trends in either helmet use or head injury may be, this paper does nothing to illuminate their relationship. I cannot even suggest that the paper is interesting; Cook and Sheikh have presented some extraordinarily dull data, from which no useful conclusions at all can be drawn. Rivara et al 2 have written an editorial marked more by enthusiasm than by a spirit of scientific inquiry. It is not clear that they have checked the arithmetic of Cook and Sheikh, as above. They are far too quick to dismiss the possibility of gathering good-quality evidence on the effectiveness of helmets. If, after the many increases around the world in the use of cycle helmets, the rate of serious head injuries showed a dramatic and regular decrease, and the use of bicycles, with its many health benefits, increased, then randomized controlled trials would not be required. Nothing of the sort has been demonstrated. Instead, we see publication of vague hand-waving and selective data use. Very few publications, despite inflated rhetoric, actually test the main hypotheses, and none have shown anything incompatible with selective quotation of the normal fluctuations in accident rates from time to time. Nor do Rivara et al address the theory of risk compensation, so well-evidenced in other areas of road safety 3,4, which renders case-control studies irrelevant in this field. Cycle helmets have no obvious useful effect on the rate of serious injuries, indeed, no clear effect on the rates of any sort of injury. When so many enthusiasts have so obviously failed to provide evidence for their pet hypothesis, I can only conclude that no such evidence is likely to exist. This finding should not surprise us. Cycle helmets were never designed to protect against injury from vehicles, which cause almost all deaths among cyclists 5, and presumably a large majority of serious nonfatal injuries. One may reasonably doubt if any practical helmet would help most of those severely injured by a motor vehicle. It is common experience that cycling in fast motor traffic is extremely dangerous, in that a very minor lapse of attention can easily be fatal. Therefore, only small changes in risk-taking would be needed to overcome any protective effect that helmets might have in saving lives. It is obvious that a few road users who think themselves more protected - or find themselves mildly discommoded by a helmet - may occasionally undergo a small extra risk far more significant than any protection that cycle helmets may actually provide. Helmets are also expensive and uncomfortable; it is hardly surprising that they seem to reduce healthy exercise. Cycle helmets seem to offer no advantages to the public health. The real issue is the dangerous state of the roads, almost entirely due to the ill-managed use of cars. This is a problem of systems not of individuals; the system includes the majority of doctors (and, sadly, myself) who drive cars regularly, but might like to be fitter and healthier. Blaming individual victims by asking them to wear helmets is not a useful answer to a serious problem. Perhaps the BMJ should invite experts such as Mayer Hillman6, Robert Davis4, or John Adams3 to review the evidence and suggest editorial conclusions? Yours, Richard Keatinge 1. Cook A, Sheikh A. Trends in serious head injuries among cyclists in England: analysis of routinely collected data. BMJ 2000;321:1055 ( 28 October) http://www.bmj.com/cgi/content/short/321/7268/1055 2. Rivara FP, Thompson DC, Thompson RS. Editorial. BMJ 2000;321:1035-1036 ( 28 October ) http://www.b mj.com/cgi/content/full/321/7268/1035 3. Adams J. Risk and freedom: the record of road safety regulation. Transport Publishing Projects, Cardiff, 1985. 4. Davis R. Death on the streets.: cars and the mythology of road safety. Leading Edge Press, Hawes, 1992. 5. Gilbert, McCarthy M. Deaths of cyclists in London 1985-92: the hazards of road traffic. BMJ 1994;308:1534-1537 (11 June); http://www.bmj.com/cgi/co ntent/full/308/6943/1534 6. Hillman M, Cycling offers important health benefits and should be encouraged. BMJ 1997;315:490 (23 August), http://www.bmj.com/cgi/content/full/315/710 6/490
Head injuries in cyclists 7 November 2000
Stephen Butterworth Send response to journal: Re: Head injuries in cyclists	Dear Sir - Cook and Sheikh have shown a decline in the numbers of head injuries in cyclists in the period from 1991 to 1995 and attribute it to the increased popularity of helmets. I have to declare an interest, since I enjoy cycling and would never wear a helmet; but it does all the same appear to me that if this kind of evidence is all that the helmeteers can adduce then I needn’t worry. Did no other factor change? What about the fashion for cycling on pavements, the general slowing of traffic in towns, the increase in the popularity of reflective clothing, and the change in the shape of bicycles? It is a matter of common observation that most cyclists these days no longer ride bottom upwards. They have shorter hair, too. It may sound callous to say so, but the only solid conclusion that can be drawn from their paper is that the overall risk is small. In a period during which about 20,000 people were killed in road accidents only 120, or 20 a year, died from a head injury while cycling. Moreover no one pretends that all, or even most, of these lives would have been saved by wearing a helmet. Compared with the figures for accidents in the home or at work the figure is tiny. The best way of reducing it would be by enforcing speed limits. Cycling is pollution-free and affords pleasure to millions of adults and children alike. It keeps coronary heart disease at bay and gives an occupation to many who might otherwise be indulging in street vandalism, arson or domestic violence. Like many other occupations it is safe if you do it sensibly. Wear a helmet if you want to, don’t think that it will save your life in all circumstances, and keep away from roads where nine motorists in ten are driving as if they were at Brand’s Hatch. Stephen Butterworth, MD FRCPath.
Curate's egg 11 November 2000
Simon Baddeley, Lecturer University of Birmingham, Public Policy Send response to journal: Re: Curate's egg	I welcome research that aims to contribute to saving human lives. The researchers have drawn on more recent data that shows the contribution of cycle helmets to safety. This monitoring, as road and traffic conditions change, needs to be done all the time. The results, as the BMJ comment suggests, do not address the issue of compulsion but may well be helpful to those wishing to promote legislation that would compel cyclists to wear helmets at all times when cycling. What is now needed and should be encouraged by the BMJ editors (and others) is research which explores the validity of the, often quoted, proposition that compulsory helmet use would reduce cycling so that we would lose the community health value of that activity (plus its contribution to reducing traffic congestion) in return for the health value of reduced deaths and injuries among the cyclists who would wear helmets. In addition, knowing the difficulty many parents have getting young people to wear helmets, compulsion might bring the authorities (not just the police) in on the side of parents who would permit and support children cycling so long as they knew helmet use would occur and would provide reliable protection. In this way numbers of cyclists might actually increase - challenging the proposition that compulsion will drive cyclists off the road. I know none of this was included in the research brief of this paper and I am well aware of the methodological problems of addressing the question in the form I've suggested. Nonetheless such research would take this frequently polarised debate forward in fruitful ways. Legislators and indeed cyclists like myself who are uncertain about the issue will seek answers to questions like these. In addition, I wonder if researchers who might be inclined to be dismissive of certain views on helmet use as “primarily rhetorical” and “emotive” would grasp that there are serious points to be made about responsibility for risk - even though these may not pass the test of scientific judgement. To give an example - a political calculation might be made along these lines: "I would swap the inconvenience, as I currently regard it, of wearing a helmet in return for the inconvenience to which motorists would be put by being required to obey traffic lights and observe speed limits." Such political bargains are part the social contract that occurs in public conversation in the media and a wide variety of forums. They are not of course scientific but any one seeking truth in a scientific way ought to be aware of the extent to which their research focus and results will be factored into such continuing dialogues about quality of life among cyclists, medical professionals, journalists, police officers, educationalists, parents and drivers and indeed any combination of interested and responsible citizens.
Bicycle helmets again! 13 November 2000
Anthony Campbell retired consultant physician Send response to journal: Re: Bicycle helmets again!	I am pleased to see the bulk of the replies to this article are pointing out its flaws in reasoning and are opposed to the compulsory use of helmets. I cycle regularly in Britain and abroad (in mountains whenever possible as an OCD member); I've cycled for 60 years (admittedly with a 20-year gap in the middle) without a helmet and have no wish to be forced to wear one at this stage. I find even wearing a cap is unpleasantly hot and if I had to wear a helmet I'd ride less or not at all. I'd therefore be at greater risk of a stroke or heart attack, at possibly smaller risk of a head injury. This is my choice and it should remain so. Life is made up of risks. It should be up to each of us to choose which of them we wish to incur. As many of the letters published here have made clear, the evidence in the case of helmets for cyclists is by no means so self-evident as the helmet enthusiasts would have us believe.
Dangers of Cycling 21 November 2000
Lee Jeys, Staff Grade AED University Hospital Aintree Send response to journal: Re: Dangers of Cycling	Dangers of Cycling, especially Mountain Biking Editor – Recent articles by Cook et al & Rivara et al (28/10/2000) highlight the benefits of cycle helmets for the reduction of head injuries in cycling accidents1. We feel that the public fails to understand the severity of injury that can arise from recreational cycling. In our recent study of Mountain Bike injuries presenting to the Orthopaedic Department at the Royal Shrewsbury Hospital, it was found that 84 patients [predominantly male (n=70)] with a mean age of 22.5 years, suffered significant injuries in a 12 month period. A total of 19 patients needed operative treatment (22.6%), some requiring multiple procedures with a prolonged hospital stay. The most common injury was fracture of the clavicle (13%), although this was closely followed by other shoulder girdle injuries (12%), distal radial fractures (11%). In addition some more serious, even life threatening injuries were identified. These included six patients with open and closed fractures of the femur or tibia, one of whom, an eleven year old, also had a significant head injury requiring helicopter transfer to the regional neurosurgical centre. In addition one patient sustained neurological deficit with a fracture dislocation of the 2nd & 3rd Cervical Vertebrae and required urgent stabilisation. A further patient required a life saving Nephrectomy to control haemorrhage, another patient required drainage of a significant haemopneumothrax. These serious injuries represented 20.3% of injuries referred during the study period. Both the recent articles fail to impress the high impact nature of cycling injuries, especially off road cycling. Previous reports from the USA and New Zealand, have indicated a high use of helmet wearing amongst cyclists (80-88% in off road riders) 2,3, possibly accounting for a low incidence of head and neck injuries. They concluded that the majority of off-road injuries were minor 2,3, and that the incidence of fractures was low 2. Recent reports show that we have a long way to go before we reach this level of compliance. It is important that doctors confronted with an injury associated with mountain biking, take the mechanism of injury into account and prepare for significant trauma. Injuries are usually sustained by high velocity impact into immovable objects with little or no patient protection. Further investigation is clearly indicated into the prevalence and effectiveness of body armour use(in addition to helmets), amongst both recreational and competitive mountain bikers. This may prove a valuable step in improving the safety of this sport. References 1 Trends in Serious Head Injuries among Cyclists in the UK: A.Cook, A.Sheikh, BMJ. 2000 Oct 321:1055-6 2 Injuries involving off road cycling; Rivara FP, Journal of Family Practitioners. 1997; 44(5): 481-5 3 Off-Road cycling injuries. An Overview; Pfeiffer RP, Sports Medicine. 1995 May; 19 (5); 311-25 Authors Lee Jeys – Previous Orthopaedic Trauma Fellow, Royal Shrewsbury Hospital, Shropshire Gillian Cribb – Orthopaedic SHO, Royal Shrewsbury Hospital, Shropshire Andrew Toms – Orthopaedic Specialist Registrar, Royal Shrewsbury Hospital, Shropshire Stuart Hay – Consultant Orthopaedic Surgeon, Royal Shrewsbury Hospital, Shropshire Correspondence Lee Jeys lee.jeys@btclick.com 27 Newton Park Road, West Kirby, Wirral, CH48 9XE
Re: Dangers of Cycling 22 November 2000
Ian Nesbitt, SpR anaesthesia newcastle Send response to journal: Re: Re: Dangers of Cycling	Dr Jeys in your study, what were the number of admissions of cyclists run down by cars, pedestrians hit by cars, and the number of car occupants admitted following RTAs? How did their rate of severe injuries compare to the: One head injury, one nephrectomy, one C spine injury and one haemothorax associated with mountain biking?
Cycle helmets 30 November 2000
Mayer Hillman Send response to journal: Re: Cycle helmets	Sir - The authors of the editorial "Bicycle helmets: it's time to use them" (BMJ, 28 October) are well known as advocates for cycle helmet wearing. It is notorious that the standard of evidence required by committed advocates is not as stringent as that demanded by dispassionate scientists. They offer the study by Cook and Sheikh in the same issue of the BMJ as representative of the sort of evidence that has persuaded them of the benefits of helmet wearing. The first calculation presented by Cook and Sheikh does not inspire confidence in the rigour of their study --35056 cycling injuries are 0.28% not 2.8% of 12.6 million hospital emergency admissions! The 24.2% decrease in numbers of head injuries that they report from 1991 to 1995 is presented devoid of any context. It is suggested that the decrease is attributable to increased wearing of helmets--but no evidence of the magnitude of this increase is presented. Nor is any measure of exposure provided. Between 1991 and 1995 (the years covered in the Cook and Sheikh study), the number of cyclists killed and seriously injured per 100 million vehicle kilometres increased by 8.6% while the figure for all drivers and riders decreased by 16.7% (for fatalities the figures are 0% and minus 20% respectively, Road Accidents Great Britain: 1998, Table 8). This suggests that any decrease in head injuries over this period has been more than offset by increases in other serious and fatal injuries. The authors of the editorial dismiss the effect of risk compensation on behaviour on the grounds that there is no evidence that it applies to cyclists. The evidence that risk-taking behaviour is sensitive to the risk-taker's perception of safety and danger is now overwhelming --from trapeze artists with safety nets to drivers of cars fitted with ABS brakes (for readers new to this debate, an introduction to the evidence can be found in Wilde 1994, Adams 1995, Adams 1999). Yet, Rivara and the Thompsons argue that the behaviour of cyclists is oblivious to changes in perceived risk. They appeal to two sorts of evidence. The first, based on "case-control studies", looks for changes in the proportion of people with and without helmets suffering head injuries. The Cook and Sheikh study which they cite does not present evidence on the proportion of casualties who were wearing helmets. But even if it had done so, it would not be relevant to the question of whether or not the highly advertised protection afforded by helmets might affect risk-taking behaviour. The second, curiously labelled "ecological", looks for changes over time in casualty rates. The statistics cited above suggest that, over the period of the study, cycling casualties, controlled for exposure, increased. In their Cochrane Library Review (2000), they employ the dubious tactic of attributing to one of us - Hillman - the argument that 'helmeted cyclists feel "invincible" and therefore ride in a more reckless manner', and go on to state 'We believe these arguments to be specious'. With "invincible", they attribute to Hillman a word he never used. They repeat the offence in their editorial by again attributing to him an argument he does not make --that the risk to cyclists is "unchanged" by helmet wearing. In fact, the wording of the relevant part of the Hillman text states 'Cyclists are less likely to ride cautiously when wearing a helmet owing to their feeling of increased security. In this way, they consume some, if not all, of the benefit that would otherwise accrue from wearing a helmet.' In these ways, they caricature the risk compensation hypothesis in order to dismiss it. The hypothesis proposes--with the support of abundant evidence--that risk management is a balancing act, and that safety interventions that are not accompanied by a reduction in the propensity to take risk are responded to by behaviour that tends to frustrate the objectives of the interveners. The statistics relating to cycling are meagre compared to those for motorised forms of transport, but they contain, such as they are, no evidence to support the view that cyclists are the singular exception to the rule that people respond to safety measures. Given all the evidence from other better documented activities, the onus of proof must surely lie on those who seek to argue that cyclists are unique in this respect. References 1.Adams J. Risk, UCL Press, London, 1995. 2.Adams J. Cars, Cholera and Cows: the management of risk and uncertainty, Cato Institute, Washington, D.C., 335, 1999. http://www.cato.org/pubs/pas/pa-335es.html 3.Cook A, Sheikh A. 'Trends in serious head injuries among cyclists in England: analysis of routinely collected data'. BMJ 2000; 321:1055. 4.Hillman M. Cycle Helmets: the case for and against, Policy Studies Institute, London, 1993. 5.Thompson DC, Rivara FP, Thompson R. 'Helmets for preventing head and facial injuries in bicyclists' (Cochrane Review). In: The Cochrane Library, Issue 3, 2000. Oxford: Update Software. 6.Wilde G. Target Risk, PDE Publications, Toronto, 1994. Professor John Adams, Department of Geography, University College London, 26 Bedford Way, London WC1H 0AP. Dr. Mayer Hillman, Senior Fellow Emeritus, Policy Studies Institute, 100 Park Village East, London NW1 3SR.
scottish data shows fall in head injury 21 December 2000
Adam Redpath, principal statistician ISD scotland Send response to journal: Re: scottish data shows fall in head injury	Dear Sir, Cyclists’ head injuries reducing in Scotland?   We read the paper by Cook and Sheikh on cyclists’ head injuries in England with interest. We have been able to conduct a similar analysis of Scottish data using Scottish Morbidity Record 1 (hospital discharges) for the whole 1990s. Table Discharges from Scottish Hospitals following cycling accidents . Year Head Injury Other Diagnosis Total Percentage Head Injury 1991/2 799 683 1482 53.9 1992/3 706 622 1328 53.2 1993/4 621 674 1295 48.0 1994/5 698 711 1409 49.5 1995/6 763 874 1637 46.6 1996/7 774 949 1723 44.9 1997/8 670 942 1612 41.6 1998/9 555 869 1424 39.0 1999/0 617 904 1521 40.6 Total 6203 7228 13431 46.2 The trends we see in Scotland are remarkably similar to the English picture, with both the number of discharges constant over the 1990s and that the percentage contributed by head injuries reducing fairly steadily. This trend continues in Scotland after 1995, where the English analysis stops The percentage of cyclists’ injuries recorded as head injuries in Scotland seem 10-15% higher than in England. Direct comparisons are hard as data as data collection systems are definitely different and clinical care and admission policies may be different north and south of the border.   Yours sincerely,         DR DERMOT GORMAN ADAM REDPATH Consultant in Public Health Medicine Statistician, ISD     DAVID MURPHY Senior Information Analyst, ISD   CookA, Sheikh A Trends in serious head injuries among cyclists in England: analysis of routinely collected data. BMJ 2000;321:1055.