Motoring needs role models

Lewis Hamilton models the latest fashionable motoring wear

The shocking death of 9 year old James Quackenbush has reopened the debate on whether flame-retardant motoring overalls should be compulsory. Stars from the world of motoring should stand up and take a lead on the issue.

James Quackenbush is, of course, just one of several people to have died on Britain’s roads in recent weeks while not wearing a full fireproof motoring bodysuit. Margaret Blanshard we now know died of a cardiac arrest after her Ford Fiesta collided with a lorry on the A90 in Fife; the 72 year old was too old fashioned to update her wardrobe to include a simple set of motorist’s aromatic polyamide fibre coveralls. Meanwhile, charges of causing death by dangerous driving have been dropped against 24 year old Wayne Acocks of Essex after it emerged that the driver of the Skoda Octavia that was hit by the stolen Audi R8 Acocks was driving had not been wearing motoring overalls — the Skoda driver died in hospital from multiple major trauma hours after being airlifted from the scene of the horrific high-speed smash.

But it is the case of James Quackenbush that has renewed the urgency of calls for a change in the law. It is one thing for a grown adult motorist to choose to throw away their life by not taking the simple step of donning a set of motoring overalls, but to allow a child passenger motorist to go without is quite another. AWWTM phoned grieving mother Kate Quackenbush — who left Queen Elizabeth Hospital in a wheelchair this morning — to ask how she felt as the woman responsible for the death of her own son, but the child killer declined to comment. As has been widely reported, the boy was not wearing motoring overalls when he died instantly from serious crushing injuries as the single mother’s 1998 Peugeot 205 was impacted on the passenger side by a construction waste lorry whose over-hours driver had momentarily lost concentration at the busy crossroads.

As a motorist myself, I can’t see any reason why you would not wear a flame-retardant motoring suit. I can tell you, I was very grateful I was wearing mine when I got into trouble recently. Luckily it only turned out to be a minor prang — a smashed light and a scraped panel — but I dread to think how differently it could have turned out had I not been wearing my lifesaving overalls.

Naysayers point out that most car crashes do not involve a fire, and that those which do are usually of such a severity that a flame-retardant outfit is unlikely to be of much use. To those critics we say: you’re free to make that irrational choice to go and kill yourselves if you like. For now.

And yet still many of the youngsters newly attracted to the pastime are not making the right choice. Until such a time as the law is updated, there is undoubtedly a role here for top stars from the world of motoring to set an example. Fireproof overalls have, of course, been compulsory in the professional sport for many years now. But amateur motorists need leaders to look up to. It was gratifying to hear Lewis Hamilton state his support for a change in the law in a recent press conference, but why isn’t Hamilton doing more to encourage youngsters and to help show that flame-retardant boilersuits are not just cool, they’re an essential part of any motor to school or weekly drive to the supermarket.

Our sporting heroes have a simple duty: to set an example. They must do the right things, and let people copy those right things. And one of those oh so simple little things is wearing full body flame-retardant overalls at all times behind the wheel.

Not hard, is it?

All those helmets posts in one place

Last year I went into some detail about why existing research into the efficacy and safety of helmets for cycling does not come close to the standard of evidence that is normally required and which we would usually demand for a medical intervention (which is what they are). Basically an application to helmets of all those things that Ben Goldacre bangs on about. But I never added an easy to link to contents page when it was complete. So here it is.

Killer Cures: a very brief introduction to why it is so important to do proper thorough research on medical interventions.

So what’s the best evidence we have on bicycle helmets?: a brief review of the research that has been performed on helmet efficacy — how it was done, what it found, and what the limitations of the methods were.

Headline figures: putting the relative risk figures reported by research papers into context of absolute risk.

What is a bicyclist?: looking at one of the major flaws in existing research on helmet efficacy — ignoring the differences between transport, leisure and sport cycling.

Would a helmet help if hit by a car?: a brief diversion into one of the side-arguments, but an important one given that most transport and leisure cycling deaths and serious injuries involve a motor vehicle.

Risk compensation and bicycle helmets: why it’s important to test for potential side-effects of interventions, some of the proposed side-effects, and why the research in this area also has too many limitations.

The BMA, the BMJ, and bicycle helmet policy: introducing the BMA’s position on helmets. Just one of several organisations with a dodgy position, but one that I think is particularly important/interesting.

How did the BMA get bicycle helmets so wrong?: a sort of conclusion piece, reiterating the importance of doing proper research on both the efficacy and the side-effects of medical interventions, and how an organisation which should know better managed to abandon this principle in favour of anecdotes for helmets.

Followed by some frivolous posts:

• Appendix: Bad Science Bingo in the BMA’s “safe cycling” pages
• Won’t somebody please think of the children?
• Prevention and cure
• Who are all these self-harming Dutch helmet wearers?

Who are all these self-harming Dutch helmet wearers?

Martin Porter mentions a fun fact about helmet wearing:

Hans Voerknecht has been to a Velo-City conference in Vancover to explain why mandatory helmet laws are not such a great idea.  One of his statistics is that In the Netherlands, where cycling is ubiquitous, 13.3 per cent of the cyclists admitted to hospitals with injuries wore helmets — even though just 0.5 per cent cent of Dutch cyclists wear helmets.

This statistic is both utterly useless and extremely important. It tells us nothing about whether helmets are effective, ineffective or dangerous, but it does brilliantly illustrate the fact that the helmets issue is far from being a simple “no brainer”, and hints at one of the major flaws in the scientific studies of helmet efficacy.

Martin speculates on the reason for the interesting 30 times higher rate of hospitalisation amongst helmet wearers:

Maybe tourists from Anglo Saxon nations wearing helmets are disproportionately represented in the hospital statistics.  Maybe also those with helmets are perceived by motorists or perceive themselves to be less vulnerable.

In fact, it’s obvious who the helmet wearers are in the Netherlands.

Here’s a cyclist wearing a helmet:

while this bicycle user is helmet free:

These cyclists, ready for Saturday morning training, are wearing helmets, but the woman who has just passed them isn’t:

This cyclist is wearing a helmet:

This family out for a ride isn’t:

This cyclist is wearing a helmet:

This chap just has a cap:

This guy is wearing a helmet:

This one isn’t:

These cyclists are wearing helmets:

These folks aren’t:

These cyclists are wearing helmets:

And these aren’t:

Can you spot the difference? All of the helmeted cyclists are racing around, head down, feet firmly clamped to the pedals on fragile lightweight skinny tired bicycles — except for the one on a muddy knobbly tired mountainbike. Most of the helmet photos were taken at the weekend. Some of the others were too: a couple of gents leisurely touring the sand dunes in a nature reserve, and a family crossing Nesciobrug, perhaps off for a picnic in the country. But mostly they’re just people making everyday journeys: commuters in Amsterdam, shoppers in Utrecht, school kids in Houten. They’re on sturdy steady bicycles, rarely doing more than 15mph. Their environment is not completely without hazards, but even if things do go wrong, they’re extremely unlikely to find themselves hospitalised. The racers and mountainbikers, meanwhile, are far more likely to fall off or hit something, and at the sort of speeds where that breaks things.

The Dutch wear helmets — and get injured — when they’re doing sports. The Dutch don’t wear helmets when they’re using transport.

This is one of the major flaws in much of our research on helmets, and in much of the British approach to cycling. It fails to account for the differences between using a bicycle and participating in (extreme) sports.

Edited to add, in case it wasn’t clear — for I fear that too frequently in these posts I leave all of the background as taken, having been over it many times before — in the Netherlands these racers wearing helmets are the same people riding utility bikes without them. The folk who get dressed up in lycra and helmets to ride sports bikes at the weekend will, during the week, be riding a utility bike in normal clothes and no helmet, because that’s what the Dutch do. All of them. I mean, they don’t all do the racing, but they all have a utility bike. We don’t expect folk who enjoy a bit of rock climbing at the weekend to continue wearing their helmet all week, or people whose hobby is diving to keep the scuba tank on for the Monday morning commute.

Prevention and cure

While organising notes, I stumbled upon this quote I bookmarked years ago, from the great Harvard cancer biologist Judah Folkman:

A pediatric surgeon in Boston just finished a difficult operation. To relax, he went to the Charles River and sat down on a bench. Suddenly, he heard cries of ‘Help! Help!’ and saw a person drowning. The surgeon jumped into the river and pulled the person to safety. He lay exhausted on the banks of the river and again heard, ‘Help! Help! ’ He glanced at the river and saw another person drowning. Despite his exhaustion, he jumped into the river and pulled the second drowning person to safety. Now, he was truly exhausted and lay on the ground huffing and puffing and again heard, ‘Help! Help! ’ He raised his head to look toward the river and saw a third person drowning, but he also noticed two basic researchers walking by the river. The surgeon shouted, ‘Colleagues, you must help! This is the third drowning person in the river in one afternoon! ’ The researchers looked at the river and then at the surgeon and said, ‘Three people drowning in one afternoon? This is very interesting! We’ll walk upstream to see who’s throwing them in!’.’’

(I think actually that it would work better if cast with public health researchers in place of basic researchers. The basic researchers would be too busy describing in obscure detail of the currents of the river, while translational researchers designed a better buoyancy aid for those currents.)

Folkman was applying the metaphor to his own field, cancer, but it works equally well for death and injury on our streets. The “road safety” approach to the problem has people studying the currents and advocating hi-viz vests and bicycle helmets, while spending billions on air ambulances and major trauma units. The “road danger reduction” approach goes upstream and asks why we are allowing large volumes of fast moving vehicles into the places where we live and work and play and learn. And it’s notable that in medicine, it’s the surgeons who think that preventing injury means bicycle helmets, and the public health researchers who think that preventing injury means calming and removing cars and trucks.

Here are a few of them: Danny Dorling talking about the open sewers of the 21st century; Harry Rutter’s Street Talk on moving towards a healthier city; and Ian Roberts, acting badly, on The Energy Glut. And you can hear Robert Davis talking about “road danger reduction” at London South Bank University on thursday next week.

During the 20th century, life expectancy lengthened by 30 years in the developed world. 25 of those years are attributable to public health intervention — to prevention rather than cure. But prevention disproportionately helps the poor and frequently hinders the rich. Guess which branch of medicine gets all the money.

Won’t somebody please think of the children?

In December 2005, an article of massive importance was published in the British Medical Journal. Doctors counted up the number of children being admitted to A&E with musculoskeletal injuries (breaks and sprains — many of which would have been caused by bicycle-related incidents) on summer weekends  and discovered a startling pattern. A new preventative intervention was discovered.  They authors say:

The figure shows the weekend attendance to our emergency department in June and July between 2003 and 2005. The mean attendance rate for children aged 7-15 years during the control weekends was 67.4 (SD 10.4). For the two intervention weekends the attendance rates were 36 and 37 (mean 36.5, SD 0.7). This represents a significant decrease in attendances on the intervention weekends, as both are greater than two SD from the mean control attendance rate and an unpaired t test gives a t value of 14.2 (P < 0.0001). At no other point during the three year surveillance period was attendance that low. MetOffice data suggested no confounding effect of weather conditions.

From this data on the effect of Harry Potter books on injury rate it should be blindingly obvious that countless lives would be saved if legislation made Harry Potter books compulsory — for children at the very least (we can perhaps allow adults the freedom to choose to turn themselves into dribbling brain damaged wrecks by not reading Harry Potter).

Anybody who cycles while not reading Harry Potter clearly deserves to have their brains smeared across the road. They lack any credibility.

Gwilym, S. (2005). Harry Potter casts a spell on accident prone children. BMJ, 331:1505-1506 doi:10.1136/bmj.331.7531.1505

Further reading: ‘Tis the season, from Language Log.

Appendix: Bad Science Bingo in the BMA’s “safe cycling” pages

This is just a crude brain dump of a post that comes after the serious series — posts one, two, three, four, five, six, seven and eight.

Sorry, I just can’t get over these extraordinary pages on the BMA’s website. Here’s a very quick run through some of the Bad Science Bingo points that leaped out.

There were the canards, fallacies, and methods of misdirection:

1. Obviously there’s the emphasis on anecdotes and cases, the lowest form of evidence, which are essentially appeals to emotion.
2. Coupled with that the description of the “beliefs” of a few doctors, designed to nudge readers into conformity (acting as a subtle argument from authority for readers who are not doctors, and an argumentum ad populum for those who are).
3. Specifically in a couple of the anecdotes the selective recall of serious injuries in non-helmet wearers and minor injuries in helmet wearers (creating the illusion of control).
4. “Figures from New Zealand show that in 2006 there were 883 cyclists injured and nine killed. This corresponds to 20 people per 100,000 injured and 0.2 people per 100,000 killed. These figures are lower than those reported for 1994 when legislation was first introduced.” Fun factoids, but they don’t actually say anything about helmet efficacy. Lots of things changed between 1994 and 2006. (Post hoc, etc.) Perhaps there is evidence for NZ’s legislation improving safety but the 2006 crude injury statistics aren’t it.
5. Incidentally, while we’re on correlation and causation, the authors even get their statements on cycle tracks subtly wrong: “During the period of 1976 to 1995 Germany almost tripled their mass of cycle networks and this led to a 64 per cent drop in cyclist deaths.” While the evidence of a causative link is much stronger here, it’s a lot more complicated that a simple one “led to” the other. The reference does indeed state that Germany tripled their cycle network and that their death rate fell, but it notes that the later is in part the result — directly and indirectly — of the former.
6. I loved this statement, when discussing the side-effect of reduced rates of cycling: “If legislation were to reduce the rates of serious injury and promote increased public confidence in cycling, the effect might be to make cycling more popular. Clearly, there is a need for further research on this matter.” I don’t know where to begin. After dismissing all the side-effects of helmets as being based on too weak and preliminary evidence, the BMA counter it all with a speculation based on none at all — and tell us that there is a clear need for more research. Well quite.

And there were specific claims or activities that run counter to the cited evidence, or subtly misrepresented it (I did not systematically check references, these are simply things that leaped out as contradicting what I recall of the literature):

1. On page 2 the BMA list the things they are doing in addition to promoting helmets. The first item is “publicity and education campaigns in order to raise drivers’ awareness of more vulnerable road-users, including cyclists”. We know that these don’t really work.
2. The “risk compensation” section on the fifth page cites just one source, the Spanish study described on Monday, whose study design we know can not answer the question that they are asking it to answer.
3. “As noted in Table 2 the Macpherson and Spinks 2007 Cochrane review found no evidence to either support or counter the possibility that legislation may lead to negative societal and health impacts such as reductions in cycling participation.” You would probably read this and think, “studies have been done and they found no evidence for X.” It actually means, “the studies didn’t bother looking at X.”

And there were fun inconsistencies:

1. Kirsty’s story on page 5, “Doctors believe that had she not been wearing a cycle helmet at the time of her crash, she would have died,” and on page 6, “They have been shown to reduce the risk of head injury and its severity should it occur. This does not apply to fatal crashes but in such instances the force of impact is considered to be so significant that most protection would fail.”

The resource is just generally bizarre. It has a very weird set of focusses. On one page it gives a seemingly arbitrary selection of factoids from cyclist demographics (notably absent is any acknowledgement that “cycling” is not a single activity); on another it notes the diversity of cycle helmet standards — but fails to discuss any of the important consequences of this, such as how few helmets these days meet the stricter standards that applied in the past, back when most of the evidence on helmet efficacy was collected. In a table on the fifth page they mention that a study found no evidence of helmets causing or exacerbating rotational injuries — yet this is the only mention they make of the rotational injuries problem. Their inclusion and omission criteria appears to be completely random.

Anyway, enough of this. I don’t want to hog the game — your turn.

How did the BMA get bicycle helmets so wrong?

In 1958, the UK licensed a drug for treating morning sickness. It worked very well. The studies all showed that pregnant women suffering from morning sickness received much relief with the drug. Three years later it was withdrawn, but not before 2,000 babies were born with birth defects — 20,000 worldwide — three quarters of whom would die in infancy. The drug was, of course, thalidomide. It managed to get licensed because too many of the people studying it were focused on very specific aspects of its activity on the disease states that it was thought to treat, and too few were stepping back and looking at the big picture. It prevented morning sickness, therefore it worked — the logic of the day.

Joe’s anecdatum: In 2003, Joe, an 18 year old male, slipped on some wet stairs in a block of flats. His head fell eight feet onto the concrete floor. He was not wearing a bicycle helmet. He had a headache for the rest of the evening. He has never been diagnosed with any long-term ill-effects.

A disaster on the scale of Thalidomide can’t happen these days because the path to drug licensing forces researchers to comprehensively check all effects and outcomes of a new drug. Individual researchers will know in extravagant detail very narrow aspects of how a new drug achieves its desired effect. Some of them will know the exact rate at which it crosses the various barriers into the blood and into organs; others will know the exact chain of activation of molecules and genes within cells, down the individual amino acid residues that are modified and the exact number of seconds after the drug is administered; others will know the exact schedule and mechanism by which the drug is broken down or expelled from the body. They’ll be really excited and enthusiastic about their new drug. But when somebody steps back and points out that the drug causes heart failure, it won’t get anywhere.

But the BMA seems to forget everything it knows about testing interventions when it comes to bicycle helmets. There are some superficial differences between helmets and what we normally think of as “medical intervention”. They are a physical intervention rather than a drug — but medicine deals with and properly tests physical interventions all the time. And it’s supposed to prevent rather than treat injuries — but medicine deals with and properly tests preventative measures, including conventional drugs, all the time. There is no intrinsic reason why bicycle helmets can not be tested properly, in line with the rules that were designed to prevent another thalidomide disaster. We have the methods and the expertise.

Joe’s anecdatum: In 2009, Joe, a 23 year old male, slid on the gravel on the Greenwich Peninsula Thames Path, hitting his head on the concrete path and writing off an £800 camera lens. He was not wearing a cycle helmet. He was unhappy and was bored for several hours waiting for Lewisham Hospital to glue his face back together. He stayed home all next day. He has never been diagnosed with any long-term effects.

And yet the evidence that we have on bicycle helmets is currently in a worse state than the evidence that got thalidomide licensed. There is some (limited) evidence that in people who have had crashes, helmets reduce the rate of specific types of head injury — just as there is undisputed evidence that thalidomide is effective in relieving morning sickness. But there is also (equally limited and disputed) evidence of several different side effects — an increase in other types of injury* and an increased rate of crashes (particularly crashes with vehicles, which are more likely to have negative outcomes). And there is also evidence that helmets discourage many people from cycling* — an activity that adds many quality years to people’s lives by preventing or delaying cardiovascular disease, cancers, diabetes, depression, dementia, and all those other diseases of sedentary lifestyles. Helmets might be an effective intervention for the types of injuries they are claimed to prevent, but that would be irrelevant if, like thalidomide, they cause more problems than they solve.

Joe’s anecdata: In 1991, Joe, a 6 year old male, on separate occasions smashed his head open a door, some concrete steps, and a glass coffee table. On no occasion was he wearing a cycle helmet. He has a scar on his forehead that is almost identical to James Murdoch’s. Unlike James Murdoch, he has never been diagnosed with any other long-term impairment or ill-effects.

I’m not saying that they do. The issue is not that there is overwhelming evidence against helmets. The evidence that they are the cause of crashes and other injuries is no stronger than the evidence that they prevent head injuries. The issue is that the evidence either way is nowhere near good enough to make a recommendation. If helmets were a drug, they would be nowhere close to getting licensed right now.

Which is why British doctors should be embarrassed that the British Medical Association currently lobbies for helmets to be compulsory when riding a bicycle. Imagine if a pharmaceutical company developed a drug which, if administered before receiving a specific kind of traumatic injury, makes that injury easier to treat. Imagine doctors and medical scientists lobbying for it to be compulsory for everybody to take this drug daily, without anybody ever having checked for side-effects.

How has this situation arisen?  The policy decision has largely been made on the insistence of A&E consultants and trauma surgeons.  Consider the anonymous quotations that are scattered through the BMA’s cycling pages:

‘I have seen – in my practice and when working in A/E – quite a number of serious head injuries from children falling off bicycles. I have also seen a number of children who wore helmets who only suffered minor injury. I am convinced that helmets reduce injury.’ — GP

’I would certainly support cycle helmet wearing for cyclists. I have seen far too many young lives ruined by head injuries.’  — Consultant in Emergency Medicine

’I am an Emergency Department Consultant and a keen cyclist. I wholly agree…that we need to move to an environment where cycle helmet wearing is the norm, rather than the exception’  — Emergency Department Consultant

’As a regular commuting cyclist through twelve miles of heavy London traffic and as a Consultant Emergency Physician I whole-heartedly support the BMA’s stance on the introduction of legislation to make the wearing of helmets mandatory.’  — Consultant and Honorary Senior Clinical Lecturer in Emergency Medicine

’Over the [last] 16 years I have worked in A/E. I have dealt with hundreds of head and facial injuries, particularly in children, that could have been avoided had a cycle helmet been worn. I have also had the misfortune to deal with a number of fatalities that I believe would have been avoided by simply wearing a helmet. I firmly believe that legislation making cycle helmet usage mandatory is essential.’  — Emergency Medicine Consultant and Clinical Director

‘I have worked in emergency medicine for the last twelve years. Personally I cycle around two and a half thousand miles each year and my family are rapidly becoming keen cyclists also. Prior to working in emergency medicine, I did not routinely wear a cycle helmet.

I have seen numerous examples of patients sustaining severe head injuries from which they will never recover whilst cycling at low speed without a helmet. I have never seen this pattern of pathology in cyclists wearing helmets under these circumstances.

I am aware of the recent Cochrane review on the subject. I firmly believe that all cyclists should wear helmets. I also believe that the only way to ensure this happens is through legislation. I can see no justification for allowing this entirety predictable pattern of head injuries to persist. I strongly support the BMA position…’  — Consultant in Emergency Medicine

That’s five emergency medics and a GP, all reciting anecdotes from A&E. Nobody who specialises in, say, public health.

Emergency medics and trauma surgeons are obviously very enthusiastic about the potential to put an end to injuries, just as people who were very focused on the problem of morning sickness were excited by thalidomide. But ironically, most doctors and scientists are not very good with complexity. They are good with the intense detail of their own specialism, but when they have a problem to solve they fail to consider that there might be relevant things happening outside of their own field. When emergency medics want to solve the problem of head and brain injury, they look at those injuries in isolation from the rest of medicine. It’s not their job to think about the bigger the picture, or worry about things like side-effects.

Indeed, dare I suggest that for most working emergency medics and GPs, the science of evidence-based medicine is not their job or even a major part of their training: they only need to practice what the scientists amongst them tell them to practice; most working doctors don’t need to understand how we know their interventions work.

Which is fine. But that stuff is somebody‘s job, and somebody isn’t doing it right at the BMA.

This way of thinking about the issue — as an isolated problem of emergency medicine — is reflected all through the BMA’s bizarre “safe cycling” pages, which emphasise these individual anecdotes and opinions of doctors in that field (despite “expert opinion” being frequently out of line with the science and despite everything we know about the ability of anecdotes to lead readers astray), while failing to ever think of the issues around helmets in terms of effects and side-effects or the usual path of research that is demanded for medical interventions.

The authors of the Cochrane review on bicycle helmets say, in dismissing risk compensation, “the fundamental issue is whether or not when bicycle riders crash and hit their heads they are benefited by wearing a helmet.” This is exactly analogous to saying that “the fundamental issue is whether or not when a pregnant woman has morning sickness her symptoms are relieved by thalidomide.” That is not the fundamental issue at all. The fundamental issue with any medical intervention is whether it does more help than harm, whether it improves the length and quality of our lives, whether we are better with it or without. That the authors of a Cochrane review are allowed to get away with saying otherwise is a great failure for evidence-based medicine. That the BMA think there is sufficient grounds not merely to promote this intervention but to enforce it is an epic failure.

* I thought about posting separately on these sets of side-effects too, but those posts would have been much like the rest of this series: there’s a plausible hypothesis, there’s some evidence to support it, but the evidence has limitations. Ultimately the conclusions always are: the evidence base is nowhere near good enough to support helmet promotion, let alone legislation.

The BMA, the BMJ, and bicycle helmet policy

The reason I pick up the bicycle helmet theme again this week is that the BMJ is running a sidebar poll of their readers (or, more accurately, of cycling tweeters and recipients of Robert Davis’s emails ;-)), asking whether it should be compulsory for adult cyclists to wear helmets.

The BMJ is the journal of the British Medical Association, the professional association and trade union of British doctors. Part of the BMA’s remit it to lobby the government on issues that its members believe are important, and it has some clout in this area. These policies are decided by a representative democracy — a group of members elected by region and by field. In recent years, this body has decided that it is BMA policy to support legislation that would make helmets compulsory for cyclists.

Doctors might not even have noticed the adoption of this policy.  To most it is probably an irrelevance — most people will not cycle in the conditions that prevail in this country and doctors are no exception. And I imagine that very few have read the quite astonishing “promoting safe cycling” pages of the BMA website. Readers of Ben Goldacre should get their Bad Science Bingo cards out before clicking the link.

Tomorrow I’ll dissect those pages and ask how they came to be so bad. But there is a more basic issue here. Never mind whether helmets are effective or not, aren’t there more important policies that the BMA should be pursuing?

In 2002, the BMJ polled readers about issues of health and road danger — a slightly more scientific and insightful survey than the free-for-all yes/no question that they ask this week, and one much better targeted to British doctors rather than every joker on the internet.  They asked readers to judge the importance, on a scale of 1 to 6, of various interventions for promoting the health and safety of pedestrians and cyclists. Helmets came out bottom of the doctors’ priority list:

Average ranking	Response
3.25	More and better cycle safety training
2.87	Compulsory cycle helmet wearing
3.42	Separate lanes for bicycles in urban areas
4.04	Traffic calming to reduce vehicle speeds in urban areas
4.04	Reduce car use by better public transport and by encouraging walking and cycling
3.85	Banning motorised vehicles from towns and cities

Interestingly, helmets for cyclists was ranked as only a slightly more sensible solution than helmets for pedestrians. Indeed, the results for pedestrians look much like the results for cyclists.

It’s the most heartening thing I’ve read in a long time. Most doctors get it. They’re not ignoring the bull. Certainly all of the public health doctors and epidemiologists (the people with the most exposure to scientific methods, incidentally) that I know get it. The problem is not that cyclists are taking insufficient measures to protect themselves from danger, it is that they are put in danger by motorists and by the government policies and societal norms that support the mixing of fast-moving motor vehicles, including those driven by people known to be dangerous and incompetent, with cyclists and pedestrians in our towns and cities.

Alongside their policy of lobbying for legislation to compel the use of helmets, the BMA has drawn up a set of recommendations for motor-vehicle reduction. But while the former policy is actively being pursued in Westminster and in the nations, the latter looks to have fallen by the wayside, and is still stuck in 1997. Why?

Risk compensation and bicycle helmets

Some months ago I left a series on bicycle helmets hanging while I got distracted with other things. We had looked at what the best evidence for the efficacy of helmets in preventing injury in the event of a crash is, and some of the reasons why we should be cautious about that evidence. We found that if you’re unlucky enough to have been hospitalised while riding a bicycle, you’re less likely to be there with a head or brain injury if you were wearing a helmet at the time of the crash. We noted several ways in which this protective effect is exaggerated and used to mislead, we noted that reduction in injury is from a very low level anyway, and that the research so far done fails to provide any sub-analysis of very different riding styles, such as racing cyclists, mountain bikers, and utility cyclists.

We also made careful note of the fact that a reduction in the rate of head injury in the event of a crash is a different finding to a reduction in the rate of injury and death of bicyclists. We briefly began the exploration of what this means by considering the fact that helmets are not much defence against a motor vehicle.

How could a reduction in head injury in cyclists who crash not mean a reduction in injury and death in bicyclists? Well, helmets could be causing other kinds of injury in crashes. Or they could be causing crashes — particularly the worst kinds of crashes.

The latter is a particularly interesting avenue. The idea is risk compensation or risk homeostasis, a phenomenon documented in fine detail by John Adams in the 1985 book Risk and Freedom. Adams showed that advances in road safety — seatbelts, motorcycle helmets, safer vehicle designs and wider, straighter, safer road designs — are never followed by quite the cut in injuries and deaths that is predicted; that while road “safety” has improved crashes are no less frequent, and that bystanders — pedestrians and cyclists — are butchered at an ever increasing rate.  There is a set level of danger that people are willing to tolerate, and so motorists were compensating for the new safety features by driving faster and taking more risks. To put it in Adams’s technical terms, potential “safety benefits” were instead absorbed as “performance benefits”.

James Hedlund reviewed the evidence on risk compensation and came up with a set of rules for when people are likely to compensate for a safety intervention:

1. They know it’s there.
2. They know it’s a safety feature.
3. There is a potential performance benefit to be had.
4. There is freedom to realise that performance benefit.

Well cyclists know whether or not they’re wearing a helmet, they know that helmets are meant for safety, there are potential performance benefits — riding faster, through smaller gaps, in more hostile traffic, or with less caution in conditions that would otherwise advise it — and cyclists are generally free to ride more furiously if they want to. (Indeed, you may be wanting to cycle faster, in which case go ahead and use a safety feature as a performance benefit if that works for you.)

But that’s only a hypothetical reason to expect risk compensation by cyclists wearing helmets, not evidence that it actually happens. And very little effort seems to have been put into researching that — perhaps because it’s difficult to devise a properly controlled test. A study of cyclists in Spain attempted to test the idea by comparing the rate of helmet wearing in traffic law violators to the rate in non-violators, finding that law breakers were less likely to be helmet wearers, the opposite to what they say should be expected if there is risk compensation. However, this study could not control for all possible differences between the populations (“confounding variables”) — for example, helmet wearers are already a population of safety-conscious conformists, less likely to commit traffic violations, and so a better question to ask would be whether those helmet wearers acted even more cautiously when their helmets were taken away from them, and whether the non-wearers behaved even more recklessly when given a helmet. (This study is, embarrassingly, the British Medical Association’s sole reference for their dismissal of risk compensation.) A more recent study observed a set of participants behaviour with and without a helmet, using speed as an indicator of risk taking and heart rate variability as a proxy for risk perception. This study found that when helmet users had their helmet taken away, the risk taking (i.e. speed) reduced to keep the risk perception stable. However, the study only looked at 35 people, and only looked at proxy variables. Neither study is very convincing — the limitations I describe here are just the tips of the icebergs — and certainly nowhere near strong enough or specific enough to guide policy. We still have a mere plausible hypothesis with no good evidence as to whether or not it’s true.

The authors of the Cochrane review acknowledge the suggestion that risk compensation by cyclists could affect their crash rate, but believe that is unlikely. It’s interesting to see a hypothesis dismissed with the argument from personal incredulity in a Cochrane review.

What is not touched on in the review, and which is potentially far more important (given the fact that crashes with motor vehicles are more likely to kill or seriously injure), is the risk compensation effect not of cyclists themselves but of the other road users around them — i.e., of the motorists. Look again at Hedlund’s rules. Motorists can see whether a cyclist is wearing a helmet; they know that helmets are supposed to be a safety feature; they can potentially find performance benefits — they think they can squeeze through tighter gaps when overtaking against oncoming traffic, or pass more quickly, or shoot in front while turning, because if they hit the cyclist then no harm is done; and there is nothing to stop them realising that performance benefit, since the police, if there even are any, are rarely even aware of the relevant traffic rules, let alone bothered with enforcing them. There is therefore a plausible hypothesis that motorists will take more risks around cyclists who wear helmets than around cyclists who do not.

This hypothesis is made all the more plausible by the fact that, in addition to potentially making cyclists seem less vulnerable, helmets make cyclists look more competent: in surveys of motorists’ beliefs, most assume that cyclists who wear helmets are more experienced and more “responsible“, meaning that they may be driving more carefully around non-helmeted cyclists who they expect to do something silly. And motorists overwhelmingly think that cyclists should be forced to wear helmets — presumably so that the motorists can get the performance benefits of driving more dangerously around them.

The motorist risk compensation theory has famously been tested by @IanWalker in one of the most delightful experiments in the field. Walker rode around Salisbury and Bristol on a bicycle fitted with an ultrasonic distance sensor measuring the effect of a number of variables on passing distance, including rider position in road, type of motor vehicle, and whether he was wearing a helmet. Analysis of over 2,000 passes showed that motorists tended to give on average around 5-10 cm less space when the rider wore a helmet. It’s not much difference, and the effect of motor vehicle type, perceived rider gender, and rider’s distance from the edge of the road were all stronger.

But it’s important to note that there is always a distribution of passing distances — a bell curve. There are a few motorists who give a lot of room, a few who scrape past, and a lot clustered in the middle, giving a little over a metre distance. When wearing a helmet, the bell curve shifts in a little bit. The cautious drivers give a little less space, the average drivers give a little less space, and the dangerous drivers give a little less space.  It’s the latter who are now more likely to drive into you.

Walker’s research, delightful as it is, is itself not without limitations. Most important amongst them is that, when it comes to answering questions of cyclist safety, it suffers the same limitation of measuring only proxy variables: passing distances rather than actual risk of crashes and injuries. But it tells us that there is a very important reason to study more than just the isolated risk of head and brain injury in the event of a crash.

Helmets are a medical intervention, exactly like a drug or surgical procedure. They are a preventative intervention and they are a physical intervention, but neither of those are alien to medicine and to the modern methods of evidence-based medical science. And risk compensation is just a side-effect of this medical intervention, like the side-effects of drugs. The side-effects of drugs that make it to market are by definition outweighed by the beneficial effects; but ten times as many drugs are discarded during development because the research finds that either the side-effects are so big or the beneficial effects are so small that the harm outweighs the help.

The authors of the Cochrane review defend their dismissal of risk compensation by saying “the fundamental issue is whether or not when bicycle riders crash and hit their heads they are benefited by wearing a helmet.” And that’s fine if you’re in the preliminary stages of developing an intervention and you are so far only concerned with whether it has beneficial effects. But the authors go far beyond that early stage in their conclusions, recommending that this intervention be compulsory — despite there being very good reasons to suspect that there are potentially major side-effects of this intervention. They can’t have it both ways. If you haven’t bothered studying the side-effects you can’t license the drug. It might kill people.

Would a helmet help if hit by a car?

This post is part of a series: it starts with the intro to the helmets issue, then the summary of the best evidence on helmets, then a quick diversion into how dangerous cycling is and an attempt to define terms. And there’s more…

Brake, the “Road Safety” charity, say yes:

Helmets are effective for cyclists of all ages, in crashes which do and do not involve another vehicle.

That matters, because if cycling safety is in the news, journalists will go to Brake for an easy quote.

The British Medical Association also say yes:

Helmets provide equal level of protection from cars (69%) compared to other causes (65%)

This is important, because the BMA is a highly trusted organisation with political influence, and their current policy is to endorse the criminalisation of riding a bicycle when not wearing a helmet.

Interestingly, president of the Automobile Association Edmund King, who was giving away free advertising bicycle helmets in London this week, disagrees with the nation’s medics on both issues:

We don’t think helmets should be compulsory but we think there are benefits… Our view is that helmets do not protect against cars but they may protect against some of the 2.2m potholes which often are the cause of smashes into the ground by cyclists.

Carlton Reid adds a little detail:

Most bicycle helmets are designed for falls to the ground from one metre at speeds of 12mph. They offer almost zero protection in collisions between bicycles and fast-moving cars.

The risk reduction provided by helmets in bicycle crashes that do and do not involve motor vehicles is one of the few sub-group analyses that was performed in the case-control studies that are covered by the Cochrane Review, and it’s no surprise that this is the source for the BMA’s claim. In bicycle hospitalisations that did not involve cars it reported nearly 70% fewer head injuries in the helmet wearers. In bicycle hospitalisations that did involve motor vehicles there were nearly 70% fewer head injuries in helmet wearers.  A helmet is equally effective at preventing head and brain injury in crashes with cars as in solo crashes.

What makes Edmund King and Carlton Reid think they know better than the nation’s medics and road safety campaigners?  Indeed, what makes them think that they can go around claiming the opposite of the cold hard corroborated stats of the Cochrane review?

Well actually, they’re not. Not quite. King and Reid are judging helmet efficacy by a slightly different metric to the Cochrane Review.  The Cochrane Review is the looking at the set of bicyclists who have had an accident of a severity that hospitalises but does not kill outright.  The review says nothing about deaths, for example, and as the Cochrane Review itself notes, more than 90% of cyclist deaths are caused by “collisions” involving moving motor vehicles (the same proportion is found again by a separate route in the TRL review and again in NYC).  But only 25% of hospitalisations were caused by motor vehicles.  And while Cochrane suggested a whopping 85% of head injury hospitalisations (which in turn account for around half of all cyclist hospitalisations) could be avoided by wearing a helmet, the TRL review of post-mortem reports found that only 10-16% of all cyclist deaths might have been avoided.  Hospitalisations, of the sort reviewed by Cochrane, are not representative of deaths.  Fall off your bicycle and you might get hurt.  Get hit by a car and you might die.

That’s because when you fall off your bicycle, chances are you are toppling over some way — precisely the sort of simple fall that a helmet is designed for, and the sort of fall that is least likely to cause life-threatening injury to any other part of the body.  When hit by a car the body might be crushed, or thrown up and around at speeds that helmets are not designed for, and so there are many more opportunities to suffer fatal trauma to other parts of the body.

(As an aside, Brake actually get this one the wrong way ’round:

Nearly 50% of cyclist admissions to hospital are for head and facial injuries, and the majority of cyclist deaths and injuries are a result of head injury.

TRL has the answer to this one: around three quarters of cyclist fatalities did indeed involve a serious head injury.  But only about a quarter involved only a serious head injury.  The rest also involved one or more additional life-threatening injury.  The Brake claim is at best misleading.)

This doesn’t mean that the BMA and Brake are all wrong* and King and Reid are completely correct.  A car at speed may be able to cause the sort of multiple trauma that merely falling over doesn’t, but that doesn’t mean that cars aren’t also capable of causing the sort of crashes that helmets are designed for, especially in low speed city traffic.

So Edmund King is wrong**.  But within the untruth he is communicating an important truth: cars are responsible for the most serious injuries and death, and helmets will rarely help in those cases.

Brake and the BMA are correct.  But their strictly truthful statements hide the crucial details, without which they are liable to seriously mislead.

* Indeed, they can’t be wrong.  You can provide a hypothesis for why helmets might be useless in crashes with cars, but no hypothesis can trump the real world stats that say helmets are useful in crashes with cars.

** Carlton Reid is not wrong, because he specified fast-moving cars.

What is a bicyclist?

This post is part of a series: it starts with the intro to the helmets issue, then the summary of the best evidence on helmets, then a quick diversion into how dangerous cycling is. And it won’t end here…

A good review of a medical intervention starts by explaining the population being studied.  The Cochrane review of helmets for preventing head injuries in bicyclists explains that its population is the set of bicyclists who sustained an injury that was sufficiently major to make them go to the ER for treatment (and not sufficient to kill them before they could seek treatment).

The review does not explain what they mean by a bicyclist.  (And since the original papers under review are closed-access, behind an extortionate paywall, we can’t know whether those do.)  Presumably they mean people riding a bicycle at the time that they sustained their injury.

Is that people riding their bicycle leisurely along a rail trail or towpath?

Is that people touring, head down into the wind in the deserted mountains?

Is that people racing in a peloton down the dual carriageway?

Is that kids in the BMX park?

Is that mountainbikers on the downhill courses?

Is it businessmen on their Bromptons riding through the stop-start city traffic?  Old ladies bouncing down cobbled streets on their step-through upright bikes?  Village vicars doing their rounds?

Mountainbikers, city commuters, and rail trail riders are very different people exposed to completely differently environments and risks — and who have very different helmet-wearing and hospitalisation rates.  Lumping them all together is like lumping mountain hikers, sprinters, traceurs, marathon runners, city pedestrians and country footpath strollers together under the heading “walkers”.  But lump them together is exactly what the studies in the Cochrane review do, comparing the rate of head injury (as a proportion of all injuries) in helmet wearers and non-helmet wearers, and applying the results to make the recommendation that everybody should be made to wear a helmet while riding a bicycle, whatever their style and situation.  You may as well recommend Formula 1 safety gear for the drive to the supermarket.

Perhaps helmets help prevent head injuries in all people who use bicycles.  Perhaps it helps mountainbikers more than tourists.  Perhaps it’s the other way around.  We don’t know.  We could know.  The researchers could have made sure to collect the data (perhaps the data is even already there, in the medical records) and then done sub-group analyses on their data to give individual results for separate groups of bicyclists.  But they didn’t.  Why not?  Did it just not occur to them that “bicycling” might not be a single pursuit?  Or did they just assume that it didn’t matter, or that nobody would notice?  Either way, it amounts to a pretty serious limitation when you’re asking “should we legislate to ban all kinds of bicycle use except where the bicycle user is wearing a helmet?”

Headline figures

If you haven’t done so already, start from this post and work your way forward.

In rare events like bicyclist injuries, odds ratios can be used as an approximation of relative risk: that is, how much a medical intervention changes the risk of a specific outcome.  An odds ratio of 0.3 is interpreted as a 70% reduction in risk of head injury when wearing a bicycle helmet.

The Cochrane Review looked at five studies, which contained a number of sub-analyses.  There was actually a range of odds ratios found when looking at different types of injury in different groups of cyclists.  In one, an odds ratio of 0.15 was reported.

So now the headline figure is that bicycle helmets protect against a whopping 85% of injuries.  Imagine the lives that could be saved.  Won’t somebody think of the children?  The 85% figure is constantly repeated by “Road Safety” spokesmen, and reported without context by journalists.  It’s cited by the British Medical Association in support for banning people from riding bicycles except when wearing helmets.  The 85% figure matters.

Leaving aside questions over whether the 85% figure represents the real efficacy of helmets, how useful is it as a guide for how to live our lives?  Well, as Ben Goldacre puts it: “you are 80% less likely to die from a meteor landing on your head if you wear a bicycle helmet all day.”  Nobody has ever died from a meteor falling on their head*.

What Ben is saying is that relative risk is only a useful number to communicate to the public if you also communicate the absolute risk.  If you want to know whether it’s worth acting to reduce the risk of something bad happening, you need to know how likely it is to happen in the first place.

In the UK, 104 cyclists died on the roads in 2009, according to DfT stats.  It was 115 in 2008, but the trend has been downwards for a long time.  For simplicity, lets say that in future years we could expect on average 100 cyclist deaths per year.  It’s really difficult to say how many cyclists there are in the UK, because you can define it in several different ways, and even then the data that we have is crap.  You can estimate how many bicycles there are, but these estimates vary, many bicycles might be out of use, and many of us own more than one.  You can take daily commuter modal share — which would give us 1 million cyclists — but there’s more to using a bicycle than commuting, and most people mix and match their modes.  According to the latest National Travel Survey, 14% of people use a bicycle for transport at least once per week.  An additional 4% cycle several times a month, and 4% again cycle at least once a month.  Cumulatively, 32% of the British people cycle at least sometimes, but some of those are too infrequent to be worth counting.  To be generous, and to keep the numbers simple, I’ll round it down to 16%, giving us 10 million on-road cyclists in the UK.  That means one in 100,000 cyclists is killed in cycling incident each year.

To put it another way, there’s a good chance you’ll get killed if you carry on cycling right up to your 100,000th birthday.  (If you do not first die in the inferno caused by the candles on the cake.)  Or, if when Adam and Eve first left Africa 200,000 years ago they had done so on bicycles, there is a good chance that at least one of them would be dead by now.  Alternatively, if you accept that life expectancy is around 80-90, make the unlikely assumption that all cyclists remain cyclists pretty much from cradle to grave, you might die cycling once in over a thousand lifetimes.  Nine-hundred and ninety-nine lifetimes in a thousand, you will die of something much more probable.  Like heart disease, or cancer.

But not everybody who dies on a bicycle dies of head injuries, and not everybody who dies of head injuries sustained while riding a bicycle would be helped by wearing a helmet.  The DfT/Transport Research Laboratory have done their own extensive review of the medical literature on helmets and say: “A forensic case by case review of over 100 British police cyclist fatality reports highlighted that between 10 and 16% of the fatalities reviewed  could have been prevented if they had worn an appropriate cycle helmet.”  This is because, while some form of head injury was involved in over half of cyclist fatalities, the head injury was usually in combination with one or more serious injury elsewhere on the body; and even in those where only the head sustained a serious injury, as often than not, it was of a type or severity that a helmet could not prevent.  There are, of course, many caveats and limitations of such an estimation, which relied on many assumptions, some amount of subjective judgement, and a limited dataset which was biased to the sort of cyclist fatalities that the police are interested in.  So we could be generous and round it up to 20% — that helps keep our numbers simple.

So we’re talking about about 20 lives saved per year, or in terms that matter to you, your life saved if you cycled for half a million years. Of course, a third of British cyclists already wear helmets, so we can add the number of cyclists whose lives are already being saved.  We could be generous again and say 40 lives per year.

That would give you a chance of less than 1 in 2,500 that, as a cradle-to-grave bicycle user, bicycling from nursery school to nursing home, you will die in a crash that a helmet would have protected against.  The chances are 2,499 in 2,500 that you will die of something else.  Like the 4 in 2,500 chances of being killed in a cycling incident where a helmet would not have helped.

Or the 6 in 2,500 chances of death by falling down stairs.  Or the 3 in 2,500 of being run over by a drunk driver.  Or the whopping 30 in 2,500 chances of dying of an air pollution related respiratory disease.**  Unfortunately I couldn’t find the British Medical Association’s policy on legal compulsion for users of stairs to wear appropriate personal protective equipment.

Of course, in addition to the 100 cyclists killed on British roads each year, another 1,000 suffer serious but non-fatal head injury, sometimes involving permanent and life-changing brain damage (as do users of stairs).  The Cochrane Review says that up to 850 of those injuries would be avoided or less severe if a helmet were worn; the more pessimistic TRL review says that perhaps 200 of them might be prevented or mitigated by an appropriate helmet.  Either way, we’re still in the area of many thousands of years spent cycling.

Whether you think those numbers make helmets worthwhile  it is up to you — I don’t think these numbers alone objectively prove that helmets are or are not worth using.  Just don’t be fooled by the stark headline-grabbing figure of 85% risk reduction.  When the absolute risk to begin with is smaller than that for fatally falling down the stairs, and a fraction of one percent of that for cancer and heart disease, consider whether risk reduction matters.

Of course, that might all change once we’ve looked at the next part of the story…

—

* I have not checked this fact, which I just made up, but I would be surprised to hear that it is not true.

** Hastily googled and calculated headline figures for illustrative purposes only; again, I have not thoroughly assessed these.

Final disclaimer: this is a hastily scribbled blog post, not an academic paper.  I’ve checked my zeroes and decimal places, but if I’ve overlooked something or accidentally written something to the wrong order of magnitude, please do point it out.

So what’s the best evidence we have on bicycle helmets?

According to the Cochrane Collaboration — the source that most doctors will go to for their summary of the evidence — it is five studies from the 1980s and 1990s.

The Cochrane Review set out to answer a very specific question: “in the set of people who sought Emergency Room treatment having had a bicycle crash, did wearing a bicycle helmet correlate with the rate of head and brain injuries among the patients?”  These are important details — the question was not “in the entire set of people who ride bicycles, does wearing a bicycle helmet affect mortality, life expectancy, the rate of serious injury, or injury recovery?”  It’s not a bad question that the researchers are asking, but it is a very limited question — the data is restricted to the type of injury that is serious enough to send people to hospital, but not serious enough to kill outright; it does not ask whether helmets correlate with any other types of injury beyond head and brain (more later); and it can say nothing about whether helmet wearers and non-helmet wearers differ in their behaviour or exposure to risk of the type of accident that sends them to hospital in the first place.  The latter possibility turns out to be a very interesting one, which will be explored later.

The Cochrane Review searched the existing medical literature for high quality studies that were theoretically capable of answering their question.  There are several different ways that one could design a study to answer a question like the Cochrane question — some methods more reliable than others.  The Cochrane Review found five studies described in seven papers, all with the same design: case-control studies.  This study design looks at a set of people who have been hospitalised with head injuries while riding a bicycle and examines their records to find out whether whether more or fewer of them were wearing a helmet than a similar set of cyclists who were hospitalised at roughly the same time and place but whose injuries were not head injuries.

Case-control studies have a number of limitations that make them less reliable than other study designs, like the gold-standard randomised controlled trial design.  Principally, the study must merely make the assumption that the “case” population and “control” populations are essentially the same, differing only in the intervention tested (helmets) and potentially in the outcome of interest (head injury as a proportion of all injuries).  The method accepts that there may be other differences between the populations of patients (are helmet wearers on average richer, middle class, more likely to have health insurance, I wonder?), but makes the assumption that those differences are not important to the question being addressed, and so uses statistical methods to attempt to minimise their effect on the results.  For this reason, case control studies are considered to be relatively weak evidence, and when more rigorous trials are conducted, they often find that case control studies exaggerate the effects of interventions.  A good Cochrane review will carefully pick the studies that it includes, eliminating case control studies unless they do everything possible to minimise the limitations of the design, and this review appears to have done that.

The populations in the five studies reviewed were 1040 cyclists hospitalised in Cambridge UK in 1992; 1710 cyclists in Melbourne in the late 1980s; 445 child cyclists in Brisbane in the early 1990s; 668 cyclists in Seattle in the late 1980s; and a further 3390 in Seattle in the early 1990s.  The results therefore apply to the shape, style and construction of the helmets that were on the market in the mid-1980s to early 1990s, and to the types of people who were choosing to wear helmets at that time.  (The Seattle study, completed in 1994, does look specifically at”hard shell”, “soft shell” and “no shell” helmets, finding the same result for all three).  Note that the Cochrane review was assessed as “up to date” in 2006, meaning that the authors do not believe that there is any good quality data newer than the early 1990s.  I’ll let you decide whether these studies are relevant to your own 2010-model helmet or not.

The outcome of the case control study is the odds ratio — a measure of the strength of association between the intervention and the outcome, i.e., how big an affect the intervention appears to be having, and whether it appears to be helping or harming.  It’s literally the ratio of the odds of head injury in hospitalised helmet wearers to the odds of head injury in hospitalised non-helmet wearers.  So an OR of 1 would mean that the odds of head injury were equal, while an OR higher than 1 would mean that hospitalised helmet wearers had a higher rate of head injury than hospitalised non-helmet wearers and an OR lower than 1 would mean that helmet wearers had the lower rate of head injury.

The five studies under review all agreed on odds ratios in the region of 0.3, meaning that hospitalised helmet wearers had considerably fewer head and brain injuries than hospitalised non-helmet wearers.  It’s a significant result.  Not something that often happens by chance — especially repeated in five different studies.  In the set of cyclists who turned up at the Emergency Room, there was a strong correlation between whether one wore a helmet and whether one had a head injury.

That, according to the Cochrane Collaboration, is the best evidence that we have on bicycle helmets.  In the population of hospitalised cyclists in four cities in the late 1980s and early 1990s, there was a significantly higher rate of head and brain injury in those who were not wearing a helmet.  Nothing about mortality or life expectancy.  Nothing about injury recovery.  Nothing about injury and hospitalisation rates in the whole population of cyclists.  That’s not a criticism of the Cochrane Collaboration or it’s review: they are reviewing the best evidence we have.

Evidence that is, apparently, sufficient for the British Medical Association to campaign for compulsory use of a medical intervention.

Those are just the obvious limitations of the question being asked and the study design used to answer it.  The less obvious limitations are where it really gets interesting.

Killer cures

What kind of moron does not wear a helmet whilst riding a bike? Anyone that stupid deserves to have their brains scrapped off the road. —Dave, bloke commenting on the failed Melbourne bike share.

Cycle in London without a helmet?  You’d need your head examined… —Ross Lydall, Evening Standard transport correspondent.

The BMA, as a part of its policy to improve safe cycling supports compulsory wearing of cycle helmets when cycling for children and adults. —The British Medical Association

I know a lot of you find the whole helmets thing — whether they “help” or “work” or not — tiresome and unimportant.  Well tough.  Bicycle helmets are a medical intervention — a special kind of medical intervention — and whether or not medical interventions work and are worthwhile is always a fascinating subject.  More importantly, a large proportion of the general public and of journalists assume that helmets work, and the British Medical Association campaigns for compulsory bicycle helmet laws.  What the BMA does matters.  If the BMA endorses a medical intervention, we can’t dismiss arguments about it as tiresome and unimportant.

Archie Cochrane, the influential champion of modern evidence based medicine and one of history’s most underrated heroes, is said to have played a mischievous prank on colleagues.  In an age when doctor knew best, Cochrane managed to organise a randomised trial of two care regimens for recovering heart attack patients: extensive hospital care (which every doctor knew was what a heart attack patient needed) versus home care.  A few months into the trial he convened his colleagues in the monitoring group to break the bad news that eight home care patients had died versus four hospital care patients.  His colleagues’ fears had been proven correct: hospital treatment was clearly far superior to home treatment and the trial must be stopped immediately as it would simply be unethical to continue to subject patients to dangerous home care.  At which point Cochrane took another look at his notes and declared that, to his great embarrassment of course, he had misread his shorthand: eight hospital patients had died for only four home care patients.  After the awkward silence, the monitoring group all agreed that it was far too early to draw any conclusions from such small numbers and at such an early stage — it could be pure chance that more patients died in hospital care.  The trial went on and never did provide any evidence that hospital care is any better than home care.

It seems obvious that bicycle helmets are a good thing.  They save lives.  They prevent life-changing head injuries.  If your head is fast approaching concrete, you want something to intervene.  It’s common sense, right?  You’d be mad not to wear one.

But Cochrane and his fellow mid-20th century proponents of evidence-based medicine showed that facts do not always match common sense.  The obvious answer is not always the correct one.  The obvious common sense fact that hospital care is better than home care for recovering heart attack patients turned out not to be correct.  As a new generation of doctors recognised the importance of evidence-based medicine, randomised controlled trials were retrospectively carried out on nearly everything that doctors do.  And, oops, they discovered that a lot of practices that doctors had considered to be simple obvious common sense had actually been harming their patients, ruining lives and sometimes killing people.

For a long time I took a Pascal’s Wager on bike helmets: while I had been given various reasons to believe that even if there was a benefit from wearing one it was probably marginal, there was no good reason not to wear one.  But the lesson from Cochrane — that common sense can kill you — is that there could be a very good reason for not wearing one.  What if wearing a bicycle helmet actively increases your risk of injury and death while riding a bicycle?  We can’t just assume that it doesn’t.

How could bicycle helmets possibly be bad for you?  Concrete meets head: intervention surely a good thing?  As that great 21st century populariser of evidence-based medicine would say: I think you’ll find it’s a bit more complicated than that.  In helmets, as in most transport issues, we seem to be obsessed with the engineering and overlook the way that people behave.  Helmet efficacy is as much a question of psychology as it is physics.

Because the interesting aspect of helmet research is not so much how they affect your chances surviving an accident, but how they affect your chances of having an accident.  It all comes back to how road users behave, and there are reasons to believe that helmet use could change people’s behaviour in a way that increases the accident rate.  Many readers will already be familiar with the two most established lines of research: risk compensation and the safety-in-numbers effect.  I’ll look at those in more detail another time, but briefly, risk compensation proposes that we adjust our behaviour according to perceived risks — in this case, the cyclist wearing the helmet perceives himself to be at reduced risk, and happily cycles with less care; more importantly, the car, bus and truck drivers around him drive with less care.  The safety-in-numbers effect proposes that cyclists are safer when there are more cyclists on the road — both in that specific time and place, as other vehicles will have to slow and use caution around them; and in general, as other road users will be expecting to see cyclists and are more likely to know how to behave around them.  If the perception is that cycling is a dangerous extreme sport that requires a helmet, and if that perception puts people off cycling, then the safety-in-numbers effect is diminished.

It’s easy to dismiss these things without considering them: helmets are hard but simple; behaviour is soft but complicated.  It’s easier to go with common sense.  But common sense is often what bad science is made of, and common sense can kill you.

That doesn’t mean we can just assume that helmets are ineffective or bad.  With a medical intervention, you start from scratch, collect the data, and follow the evidence wherever it takes you.  This introductory post and its title are not supposed to bias our exploration of the evidence one way or another, only to get us beyond the unexamined assumption that helmets work.

So what’s the best evidence on bicycle helmets?  Named in honour of the pioneer Archie Cochrane, the Cochrane Collaboration systematically reviews the evidence for medical interventions.  A Cochrane Review looks carefully at all of the research that has been conducted on an intervention, considers the factors affecting the quality of each piece of research, and synthesises the results of all of the research to a conclusion which will generally be considered by medical practitioners to be the best knowledge we currently have on that intervention.  In a field that must always remain skeptical of the status quo and open to new evidence, a Cochrane Review is in practice considered to be the closest approximation we have to The Truth.  Good doctors don’t use their common sense, they use Cochrane Reviews.

The Cochrane Collaboration have reviewed the evidence for bicycle helmet efficacy.  This weekend, I’ve got half a dozen posts looking at that evidence, the way that it is presented by the Collaboration, and the evidence that the Collaboration has chosen to omit.

le in London without a helmet? You’d need your head examined…Cycle in London

Weekly War Bulletin, 18 Dec

An SDLP Northern Ireland assembly member has proposed making riding a bicycle in Northern Ireland illegal except where the rider is wearing a plastic hat.  I can’t find much coverage of it, but this proposal appears to have already been delayed from August.

Also ongoing under-reported news from Northern Ireland, highlighted by Christian Wolmer this week, is the £800 million A5 dual-carriageway construction.  The bankrupt Irish government (who are already being prevented from opening another new motorway by the workers who are waiting to be paid for having built it) and the cut-happy British government are going halves on the Derry to Dublin road apparently because it makes for a nice piece of symbolic government cooperation.  I’m no expert on the Northern Ireland issue, but my understanding was that the British and Irish governments were already quite good at cooperating, and the issue is instead one of divided communities.  So what could be better than further dividing communities by driving another motorway through them?

The DfT has found that 60% of the people who are able to cycle say that they don’t because they think it’s too dangerous.  Who would have guessed?  And the road haulage industry have noticed that they’re getting rather poor publicity over all the cyclist deaths and victim that’s blame going on — but it’s ok, their PR department are on the case.

After a slow start, Bristol has allocated all of its £11 million cycle city budget.  York is still getting through its cycle city pot, with half a million on routes to and facilities in the station.

There is nobody cycling in Blackpool, therefore building cycle paths is a waste of money, say taxi drivers.  Blackpool cabbies have slammed the council for creating a road nightmare in the town.  “That’s our job,” the taxi drivers said.

Meanwhile, Boris has announced that London taxis will be electric by 2020.  I expect this to happen about as much as anything else that Boris has promised to make happen.  Boris is being praised for bringing in strict rules for taxis — six month checks and an age limit on the vehicles.  No newspaper journalist seems to have noticed that all he is doing is reversing his earlier relaxation of the rules…

There’s a 46% rise in those unregulated First Capital Connect season ticket prices outside of central London.

Northamptonshire’s road safety partnership is the latest to run out of money and switch off its cameras.

36,000 Motorists break speed limits at Gateshead Metrocentre.  None prosecuted. The Metrocentre, largest “shopping and leisure complex” in Europe, looks horrible: wide roads, dual carriageways, and acres of car parks.  And they’re surprised that people drive too fast in this sort of environment.  (I notice that 200k of the Bristol cycling city money went on a bike path to Cribbs Causeway, a similar out-of-town motorway-side “shopping and leisure complex”, when the goal should really be to reverse these awful soul-destroying developments.)

A kitten was thrown from a car on the M1.  And somebody’s throwing snowballs back at the motorists.

An Oxford Tube intercity bus fell over after taking the wrong exit from the motorway.

Two pedestrians were killed by a Range Rover driving on the pavement in central Glasgow.

The Waterloo cycle hire station is open.  I used it last night, and then ran for the train — ten minutes had been wasted running around the Picadilly area trying to find a bike in the first place.  Could you put some on Albemarle Street please?

Fat coppers break their bikes.

Nice acceptable middle-class crime: while local authorities have to cut services, Westminster are owed £18 million by people who think the world should organise itself around their Mercedes.  Meanwhile in Kent, nice middle-aged Jaguar owners have a bit of fun killing people on the motorway.

Wanking behind the wheel gets you a driving ban.  Mobile phone use not considered an equivalent offence.

For the benefit of vulnerable road users, the US are setting minimum noise levels for electric vehicles, which will presumably amount to a de facto global standard (unless and until another major car purchasing nation sets a stricter standard).

Delightfully absurd transport solution of the week?  A system of delivery tubes under Croydon.

A special bumper pack of zen: first, via RailwayEye, a Christmas carol flashmob in Sheffield station:

And via Going Underground, Christmas carols at Charing Cross:

Finally, via Hembrow, this delightful 1960s video of trains in the snow: