Thursday, 19 August 2010

Brain injuries and the Dutch cyclist

An Australian reader pointed me at this document which is about head and brain injuries amongst Dutch cyclists. Yes, there are also some people in NL who think that helmets for cyclists are a good idea.

Rather than reacting emotionally we have to look at the numbers to make sense of this. The overall risk to Dutch cyclists (it's on page two of the document) of a "head/brain injury" is 153 per billion kilometres ridden. That means that one such injury is one per 6.5 million kilometres ridden.

On average, every Dutch person makes a trip by bicycle 5.6 times per week. This works out as an average across the whole population of 2.5 km cycled every day. That's the highest figure for any population in the world. If we assume that people cycle every day of their lives to the age of 80, and that they cycle that 2.5 km every day of their life, they will ride a bike for a total of 73000 km during their lifetime. Divide it into 6.5 million and you find a figure that a typical Dutch cyclist can expect a "head/brain injury" once every 90 lifetimes.

Note that it doesn't say how serious the injuries have to be in order to be included. However, it does give total numbers of head/brain injuries per year as 550 + 1600 = 2150 which is more than ten times the total deaths of cyclists per year from all types of injuries. For the sake of making the maths easy, let's lazily (and very inaccurately) assume that every death when cycling is due to a head injury. We then find that the risk of death due to head or brain injury when cycling is actually around once per 900 lifetimes.

Also, note that the article points out that cycle helmets can only reduce the rate of deaths due to head injuries by 29%. So, if a helmet is worn by that typical Dutch cyclist, it will save his/her life every 3100 lifetimes or so.

Death occurs once in every lifetime. i.e. Other causes of death are more than 3100 times so significant as deaths due to cycling without a helmet and that applies even in this country where there is more cycling than in any other. It applies even if for the sake of simplifying the calculation we make the horribly inaccurate assumption that cyclists never die of any type of injury. This in a country where 93% of the population rides a bike at least once a week.

To summarize, deaths due to head injuries while cycling are not a major public health issue and should not be treated as such. Helmets are not the answer to cyclist deaths. Good infrastructure is what makes cycling safer.

A contrast with another cause of death:

A couple of days ago I saw some other statistics, about a much more common cause of death and injury. This covered the risk of car crashes to Britain's children. In this post is the alarming statistic that one in 27 children in Britain, more than one in every classroom, can be expected to be killed or injured in a road crash by the time they are 16.

Think about it. If the risk is similar in other age groups, then there is a chance of one in five that you will be injured or killed in a road crash during your lifetime. That's a risk due to motor vehicles which is many times greater than that faced by cyclists in the Netherlands not wearing a helmet.

Britain's roads are actually amongst the safest in the world, for drivers. However the risk of death or serious injury from road crashes elsewhere is higher in every other country than this one, where there are more cyclists than in any other country.

Previously I covered the efforts that car manufacturers have put in to make driving appear safe.

Also... 2.5 km per day may not sound much, but this is the highest average cycling per day per person figure for any country in the world. It's the average distance cycled for absolutely everyone, all age groups, through the entire year, averaged across an entire lifetime. By comparison, English speaking countries all hover around 0.1 km per day by bike per person (look it up if you don't believe me). In all places, keen cyclists of course cycle a lot more than the average. Long distance journeys by bike are also more common in the Netherlands than in any other country.

28 comments:

Nils2 said...

Hi! Not to forget, also motorists suffer from head injuries. In car crashes, head injuries are the second most common cause of death. This is described in a recent french study, The fatal injuries of car drivers.

Injury codes AIS 4, 5 or 6 (AIS 4+) were deemed possibly responsible for death. [...] For the AIS 4+ injuries, the three most frequent locations (or associations) were the thorax alone (30% of subjects), the head alone (23%) and a combination of the two (18%).

Mark said...

I cannot crunch numbers like you can David, but your calculations do show even to me why the Dutch (myself included) perceive helmets as something completely unnecessary. The risk is so incredibly low that you can rightfully take it. Especially since we all (have to) take other risks that are much bigger. The ‘common sense’ factor works the other way around in this country. Since we all cycle so much and for so long (in my case every day for over 40 years now) you know from experience how safe it is. And then there is the question of what good a helmet could do anyway. I do know people get hit by cars. I was in a collision once myself. A right turning car that overlooked me going straight on. (Those were different times in 1980!) My bike was a total loss (frame displaced) so it was quite a severe hit, but I could just not sit for a week because I had landed on my tailbone. A piece of flimsy plastic on my head would not have made any difference there. As it won’t in so many other cases.

Edward said...

As ever, the voice of reason.

Krakonos said...

"Divide it into 6.5 million and you find a figure that a typical Dutch cyclist can expect a "head/brain injury" once every 90 lifetimes."

But this also means that one out of 90 cyclists will suffer from a brain injury. And that is no small number. And this is for the average rider, who rides about 2.5km per day or about 1000km per year. It means for the people riding 5000km per year (I bet those are still very many people) the lifetime risk of a brain injury is 1 in 18! Although I'm also not a strong proponent of helments myself (I usually wear mine in the city where its mostly vehicular cacling but not on tourist bike routs) the numbers you came up with are not exactly an argument against helmets!

Krakonos said...

Oh, I forgot, don't get me wrong. I know the car is the bull here, which shouldn't be ignored, as the british statistics show. And of course in the end car driving should be made safer to others (less and slower and whatever else it takes). I'm just saying I don't think your numbers are low! Although the other numbers with the british children are of course outrageously high.

Frits B said...

The concluding sentence of the SWOV report: "All in all, the SWOV has concluded that a bicycle helmet is an effective means of protecting cyclists against head and brain injury."
Yes, of course. It also saves anybody from serious injury when a mugger hits you over the head. I'm going to buy one this instant.

freewheeler said...

"Britain's roads are actually amongst the safest in the world."

But that is surely only true for those who travel inside motor vehicles. The idea that Britain's roads are safe comes in for severe critical scrutiny from cyclist Bob Davis here.

John Adams has long put forward a
risk compensation hypothesis, basically arguing that making drivers safer (seatbelts, rigid steel safety cages, airbags) results in them taking even greater risks in the knowledge (or the unconscious knowledge) that they are personally protected from the consequences of their risk-taking. Adams argues that the seat-belt legislation transferred risk from those inside cars to those outside them, i.e. pedestrians and cyclists.

Anonymous said...

My own assessment is that a well fitting cycling helmet will limit grazing to the head if you should fall off. I wear cycling gloves for much the same reason. Friends who have tested this theory also consider it true. My advice would be make your own mind up but clearly if you potter around within a safe environment the risk and outcome of falling off is much less than if you ride fast and take some risks.
I can imagine the Netherlands appearing on charts in the marketing rooms of the helmet producers, a good opportunity to sell a few million euros worth of product but there is nothing wrong in that. I am gratefull for the good choice of cycling attire that we have today. Only when it becomes compulsory does the issue potentially become a threat to casual cycling.
Mark Garrett, Bristol UK

cmatthei said...

Statistics are a strange thing. You can proof nothing and everything with it. A flood or other natural disasters that should occur once in a century can occur two years in a row without proofing the statistics wrong.
I totally agree that nobody should be forced to wear a helmet. But I had nasty bicycle accidents myself where my helmet helped a lot. Maybe it just have something to do with subjective safety?
But you are right - there are much more important issues and greater risks in the life of a cyclist.
When somebody feels more safe with a helmet and rides more - so be it.
When somebody feels more comfortable without a helmet and rides more - so be it.

mtnpauls said...

Wow - very interesting post!!! I struggle internally with the helmet issue daily. I believe they are required where I live but the law isn't enforced as far as adults are concerned. I only wear a helmet on long distance rides and in the dark. I thank you for the info!!!

David Hembrow said...

Krakonos: You said "But this also means that one out of 90 cyclists will suffer from a brain injury."

Actually, that's not quite true. One in 90 will have a "head or brain injury" in their lifetime - but it doesn't say how serious these are. Many will be very minor injuries, and in any case the best protective effect of a helmet in any situation according to the study is just 45%, so you can't reduce this even by half.

I've bumped my head before when I've fallen from a bike, but not (so far as I can tell) caused a brain injury.

And yes, I agree that those who ride more probably have a greater risk. I ride much more than 10000 km per year myself, so I guess I inevitably run a slightly larger risk. The degree of preventable risk should I wear a helmet all the time is still very small compared with other risks in my life.

I also find it interesting that the study shows the greatest risk of head injuries per km travelled is not to children but to pensioners.

kfg said...

"Note that it doesn't say how serious the injuries have to be in order to be included/ Also, note that the article points out that cycle helmets can only reduce the rate of deaths due to head injuries by 29%."

I assume, because it is the usual practice, that the absolute number injury statistics include simple concussion. An injury that the standard bicycle helmet cannot prevent. It is designed to MITIGATE brain injury at the borderline between permanent brain damage and fatal brain damage. Below the severe impact threshold banging your head into the inside of your helmet is much the same thing as banging your bare head into a wooden beam.

I have talked to a number of people who say they wear helmets because their greatest fear is becoming a "vegetable." That they would rather be dead than seriously and permanently brain damaged. But the chance of becoming a vegetable is INCREASED by a helmet, because the people who promote them would rather see you a vegetable than dead; so that's the way they design the helmets.

So bear in mind that a significant percentage of that 29% of (hypothesised)saved lives would be spending the rest of their lives wearing helmets all the time; with attached drool cup.

As far as I am concerned you may wear a helmet or not, as you see fit. I simply believe that you should make that decision on an informed basis; based on real world physics and engineering and not, as is done in the majority case, by adopting a fetish item which you believe is imbued with powerful mojo.

To paraphrase the great philosopher Inigo Montoya; You keep using that item, but I do not think it does what you think it does.

kfg said...

P.S. @ Anon; "My own assessment is that a well fitting cycling helmet will limit grazing to the head if you should fall off. I wear cycling gloves for much the same reason."

And a simple cap made much like your glove will accomplish the same affect; and because it is made to accomplish that particular protective task will do so much BETTER than the standard road helmet. Just because you wish some sort of head protection doesn't mean you have to invoke "helmet." Depending on your particular circumstances and specific desires for protection you might well be better off, in real world terms, wearing a Stetson Boss of the Plains or an Akubra Snowy River.

dexey said...

I've twice come off a bicycle while helmetless and hit my head hard enough to have wished I had been wearing a helmet. I wear a helmet on my bikes and sometimes on my trike.
I don't care whether others wear them or not but I won't be wasting time and energy fighting any proposed helmet law. I don't recall cyclists lobbying against the UK introduction of compulsory helmets for motorcyclists and because of that law, I believe the case against is already lost.

kfg said...

"I've twice come off a bicycle while helmetless and hit my head hard enough to have wished I had been wearing a helmet."

Then why aren't you brain damaged/dead yet? The question is not facitious.

"I don't recall cyclists lobbying against the UK introduction of compulsory helmets for motorcyclists"

Perhaps they have become too pussified to protest in the UK (or perhaps you just weren't paying attention); here in the US the fight has been going on for decades, with regular, organized mass civil disobedience in protest against the laws. There have even been some wins and laws defeated, put into abeyance or repealed.

I've never been surprised at the statistics about the lack of efficacy of bicycle helmets. I understand them too well to be surprised - but what I admit DID surprise me as the statistics started to come in is that they are about the same for motorcycles. Either there is no statistically significant decrease in head injuries, or there has been a small INCREASE.

You have to remember that you can't get something for nothing. The wearing of a helmet to mitigate one risk inherently introduces new risks CAUSED by the helmet. What the statistics suggest is that the risks introduced are equal to or greater than the risks mitigated.

Now where this comes into play in a situation such as your own is how anecdotal evidence can color one's perceptions about risk in a way that does not match the realities of the world.

It is likely that what is happening is that a few lives ARE being saved by helmets; thus people are led to believe that helmets save lives - but at the same time the helmets are also TAKING lives in near equal numbers.

In other words, helmeted or non-helmeted your risk of suffering a fatal head injury is controlled by nothing but - LUCK. Your TOTAL risk is the same either way.

freewheeler said...

Dexey, it is indisputable that where cycle helmet wearing is made compulsory the rate of cycling declines. Fortunately in the UK there are no plans to introduce legislation.

You say, "I don't recall cyclists lobbying against the UK introduction of compulsory helmets for motorcyclists and because of that law, I believe the case against is already lost."

Your logic seems tortuous. It is not obvious why cyclists, who have quite enough issues to campaign on, would want to involve themselves in legislation affecting bikers, unless it directly impinges on cycling. In any case, motor cycle helmets are quite different to cycle helmets. Cycle helmets are pathetically flimsy, unlike motorcycle helmets. Motorcyclists are far more exposed to risk in so far as they travel at very much higher speeds than cyclists.

dexey said...

kfg said...
"Then why aren't you brain damaged/dead yet? The question is not facitious." It isn't facetious? Ok, then statistically, I'm led to believe, the chance of brain damage is small? The helmet, however, I believe, helps mitigate against the black eyes and broken spectacles that I have suffered.

freewheeler said...
"Your logic seems tortuous. "
What, more tortuous than "I don't want to wear a helmet so I'll ignore the good they can do and promote the alleged harms"?
Seems unlikely, but as I said I don't care if people wear them, or not. However, in the UK the precedent for introduction is already there and I doubt that cyclists are a more effective lobby group than motorcyclists.

Edward said...

Freewheeler is absolutely correct. When helmet laws were introduced here in Australia, that is exactly what happened. Helmet wearing went up to about 95% of cyclists but there has been no discernible reduction in head injuries relative to other injuries since then. Cyclists numbers fell substantially though and have never really recovered.

The indisputable fact for me is that the safest place to cycle is the Netherlands and it has nothing to do with mandatory helmet laws. Those countries with mandatory helmet laws (especially Australia) do almost nothing else to make it safe to journey by bike. There are token white lines in gutters which are called bike lanes and educational campaigns like "a metre matters" and "share the road", none of which has worked.

It reminds me of the National Lampoon film about the European holiday. Eric Idle was a cyclist who seemed to be run over by Chevy Chase in every second scene. He'd get up and say things like "not to worry" and be on his way.

That is the attitude we have to cyclists here. They are forced to share the road with fast moving cars and trucks and use joke bike lanes that send them straight into the path of opening car doors. But it's ok you see because they are wearing a helmet so not to worry.

Mandatory helmet laws are a total cop out and they do not work. Do not believe the marketing.

Brent said...

"I've twice come off a bicycle while helmetless and hit my head hard enough to have wished I had been wearing a helmet."

It's curious -- I also fell while skiing a couple of years ago, and hit my head so hard that I wish I had been wearing a helmet. Except that, well, I was wearing one!

Hitting the ground head first, helmet or not, is not a pleasant experience. Bicycle helmets (ski helmets are made much the same way) don't seem to cushion to blow. In my case, I remember just being unable to control my head in the way I was used to, and smacked it pretty good. I still wonder whether it wasn't the extra weight of the helmet that made me hit the ground, or whether I was better off with the lid. It may be impossible to know.

kfg said...

"The helmet, however, I believe, helps mitigate against the black eyes and broken spectacles that I have suffered."

Both faith and solipsism have been discredited as a means of protecting your spectacles.

During the Tour de France this year a rider crashed and messed up his face pretty badly. The television commentator made the rather nonsensical observation that, "It was a good thing he was wearing a helmet or his face might have been more badly damaged," or words to that affect, rather than the sensible one, "It's too bad that road helmets don't offer any protection against facial injuries."

There has been ONE fatality caused strictly by a head injury in the entire history of the Tour, which was ridden for nearly a century without helmets (and the medical examiner explicitly stated that a helmet would have done little to nothing to mitigate, the impact was so severe. The rider was traveling downhill at nearly 100 kph). There have been many, many messed up faces; and yet nothing is being done about this. The incidence and severity of messed up faces has not decreased in the years since helmets have become mandatory.

If you wish to protect your spectacles from being broken by direct impacts from the front, I believe you would be better served by selecting an item designed to do that, rather than one designed to protect your brain from indirect fatal accelerations by impacts to the top. These are widely available in any general sporting goods store as there are sports where this is a common occurrence.

If you wish to be protected from "boo boos" such as bruising, you will need to wear something that covers more than your head. Perhaps an Ursus MkVII.

If you think that broken spectacles and "boo boos" such as bruising are a serious public health issue that needs to be dealt with by legislative fiat across entire populations; you're a nutter.

""I don't want to wear a helmet so I'll ignore the good they can do and promote the alleged harms"? "

Ahhhh! You ARE not merely one of the faithful, but are a True Believer(tm).

Go back to the congregation in peace, Brother. Say "hi" to Pascal for me.

Anneke said...

I was hoping not to enter this discussion, but I can't stand bad logic. So.

""I don't want to wear a helmet so I'll ignore the good they can do and promote the alleged harms"? "

Turn that sentence around and you have the same argument for the other side of the discussion.

""I want to wear a helmet and I'll ignore the bad they can do and promote the alleged profits"? "

Come on. If you can't produce evidence either way, don't make statements that are empty.

If the evidence is that head injuries stay at the same level regardless of helmet wearing, than clearly helmets can either do nothing, or have a negative influence. Seems very clear to me.

And as anecdotal evidence seems to count as real evidence; I have cycled my whole life. I have been in one serious accident, and some minor slips or mini crashes. In none of these accidents, major or minor, have I hit my head. I bhave fallen on my bum, my knee, and my elbow. I never broke anything, or sustained other injuries than a few bruises.

All my friens cycle every day (remeber I live in The Netherlands) and none of them have ever even mentioned having had some kind of head/brain injury. I don't know anyone who has fallen on threir heads while cycling. On the other hand, I know quite a few people who bumped their heads into cupboard doors in the kitchen. So maybe cooking helmets need to be introduced? :P

Inconvenient Truth said...

Another interesting post, David. The helmet issue always gets the hackles up in Anglo-Saxon land. But more often than not the pro-helmeters argue anecdotally, based on the "I would have had my brain mushed last Thursday if...".

As other posters have suggested, wearing a helmet or not should be a personal choice. More important are interventions by the State, and the State's perceptions of "risk". The UK is awash with "risk assessment" procedures, but as soon as we suggest structural ways of reducing "risk" to cyclists - such as providing separated cycle paths where traffic levels are highest - suddenly the Risk Assessment Consultant Industry goes all shy.

Similarly, in Germany there are certain (though not all) policemen who insist on cyclists using cycle paths on the "correct" side of the road. But as I pointed out recently to one such guy in my pigeon German, I consider the risk of crossing a busy main road twice to be much higher than cycling contra-flow on a separated cycle path.

I consider the helmet a cultural item, in the same way as some cyclists feel naked without their skin-tight shorts and lycra top. Where cycling numbers are low, as in the UK, Australia, US etc, helmet cycling culture is highly prominent anyway, due to the relatively high numbers of cycle racers compared to utilitarians. So the helmet argument comes to the fore. In countries with high cycling numbers, cycling sub-cultures are as varied as humankind. Here in Bremen, punks, pensioners, musicians, judges, plumbers, high-heeled women, rich, poor, young parents with toddlers, schoolkids of all ages, all have their own "way" of cycling. The only regular helmet-wearers I see here are cycle couriers. Culturally, I would argue their helmet is more a statement to other cyclists - "get out of my way!"

And as Freewheeler argues, as far as dealing with "cyclist safety" is concerned, helmets are a cheapskate excuse for governments NOT to build proper cycling infrastructure.

Daniel Sparing said...

David,

thanks for the excellent number crunching - i can now use this as a powerful argument.

daniel

Phil Lee said...

It should not be forgotten that if you want to avoid brain injuries, the focus should be very much on encouraging a lifestyle which minimises the risk of stroke and heart disease. More brain injury is caused by these than all traumatic injuries combined.
The only proven effect of cycle helmets is to reduce cycling rates, which has been shown to increase the chances of stroke and heart disease - and therefore brain injury.

Frits B said...

A 71 year old French woman cyclist in Almere near Amsterdam died a few days ago as a dog collided with her, causing her to fall and crack her head.
And a 62 year old woman from Alkmaar died today of brain damage after being thrown off balance by a passing German cyclist.

Makes you think: might they have been better off wearing a helmet? Statistically it would have made no difference, but maybe, just maybe ....

kfg said...

Frits; predicting the past is a bit easier than predicting the future. Reduction of risks is not about protecting individuals who have already come to a now certain harm, but rather it is about mitigating TOTAL and UNCERTAIN risks of all events that MIGHT come to pass.

In other words, you only know what accident you are going to have and thus what steps might be taken to prevent or mitigate injury form that accident AFTER it has already happened.

Certainly if you tell me the injuries that you sustained last week it is a reasonably easy job to create a device that might have some preventative or mitigating effect. It is rather more difficult to do so for the injury you are going sustain NEXT week.

In the case of brain injury though, there are some serious limitations to what can be accomplished. The device I would have designed for these poor and unfortunate people would likely be unlike any helmet that is commonly sold for cyclists; and might well be so offensive to wear that even these people would have refused to wear them with a CERTAINTY that would be required on that particular ride.

And it might well CAUSE injury in an accident that was different in some detail.

Norma said...

@Frits
I also read about the accidents and the first thing I thought was that they probably put their saddles so high that their feet couldn`t touch the ground while sitting on the saddle. That`s customary on a ladiesbike because its more comfortable to be able to stretch your legs during cycling. As I know from painful experience you`re also more likely to fall when something unexpected happens in traffic.I feel a lot safer since I put my saddle so low my feet can touch the ground when I`m sitting on the saddle.

Frits B said...

kfg: The two cases I mentioned were so exceptional that they made the news. Both ladies would just as easily have fallen to their deaths when using a chair to get something from a high kitchen cupboard - which happens a lot more. But you see how convenient it can be to base legislation on incidents.