The CycleChat Helmet Debate Thread

[Justinslow]

It is only saying "give yourself a chance".
Clearly if someone is squashed by a Lorry it won't help, but if someone falls on their bonce it may "give you a chance".

 

[srw]

Interesting statistic I came across while reading something else on Cheshire Police Twitter page:

Cheshire Police Retweeted
CheshPol taskforce ‏@CPTaskforce Oct 18


97% of fatally injured #cyclists died not wearing a #helmet. Give yourself a chance and #PutALidOnIt

This is where statistics get up my nose. Depending on how you read that, it could mean that any number of fatally injured cyclists were wearing a helmet at the time of the accident, but 97% of them later died - after the helmet had been removed. Or did the helmets disintegrate on impact, or fall off because they were wrongly fitted?

I call bullshit. Each year about 100 people die on a bike in this country. To disprove the stat all we need is to find 4 or more deaths with a helmet. Just using the minority of deaths reported here and in the press that's a triviality.

 

[Wobblers]

It is only saying "give yourself a chance".
Clearly if someone is squashed by a Lorry it won't help, but if someone falls on their bonce it may "give you a chance".

It's not the "give yourself a chance", it's the 97% figure that Cheshire police retweeted. Even the now discredited 1989 Thompson, Rivara and Thompson paper only demonstrated an 85% reduction - and that's the highest benefit reported in the scientific literature. Indeed, whole population studies fail to show any benefit. So, wherever this 97% came from, it wasn't from any reliable source. Yet here we have a police force using its position as a source of authority to propagate something which is obviously and demonstrably false - without doing any sort of checking to boot.

These are the same people who would investigate, if you were unlucky enough to have an accident in Cheshire. I have to wonder how thorough an investigation any unhelmetted cyclist would get.

 

[twentysix by twentyfive]

Indeed, whole population studies fail to show any benefit.

Have you a link to that please? Just curious

 

[MontyVeda]

Have you a link to that please? Just curious

Australia

I wonder if the prolonged wearing of cycle helmets affects memory?

 

[swansonj]

It's not the "give yourself a chance", it's the 97% figure that Cheshire police retweeted. Even the now discredited 1989 Thompson, Rivara and Thompson paper only demonstrated an 85% reduction - and that's the highest benefit reported in the scientific literature. Indeed, whole population studies fail to show any benefit. So, wherever this 97% came from, it wasn't from any reliable source. Yet here we have a police force using its position as a source of authority to propagate something which is obviously and demonstrably false - without doing any sort of checking to boot.

These are the same people who would investigate, if you were unlucky enough to have an accident in Cheshire. I have to wonder how thorough an investigation any unhelmetted cyclist would get.

Whoa - hang on a tick - the Cheshire police stat of 97% is allegedly the % fatally injured cyclists not wearing a helmet. The TRT 85% figure is allegedly the reduction in fatal accidents caused by wearing a helmet. They are, of course, both probably wrong. But they are estimates of different quantities so surely can't be compared.

 

[srw]

Whoa - hang on a tick - the Cheshire police stat of 97% is allegedly the % fatally injured cyclists not wearing a helmet. The TRT 85% figure is allegedly the reduction in fatal accidents caused by wearing a helmet. They are, of course, both probably wrong. But they are estimates of different quantities so surely can't be compared.

Quite. Cheshire police appear to be completely innumerate. Can someone who is active on twitter call them out?

 

[shouldbeinbed]

Quite. Cheshire police appear to be completely innumerate. Can someone who is active on twitter call them out?

They have failed to reply to my questions raised by that tweet so far.

 

[velovoice]

What I want to know is, of those 97% unhelmeted cyclists, how many died of a head injury?

Let's not forget, the kinds of head injuries that helmets may confer some protection against are non-fatal ones.

(I'll pre-empt calls for sources by citing -- yet again -- the abundance of studies analysed on the cyclehelmets.org website.)

 

[velovoice]

@dmin, please could you amend URL in my last post to cyclehelmets.org (with an "s", please)? Thanks.

 

[swansonj]

In which case, can i make the only mildly provocative comment that I increasingly don't think cyclehelmets.org is a reliable site.

I oppose helmets primarily for what you might call strategic and political reasons: that I don't think it serves the long-term interests of society or of the individuals that make it up to promote helmets with all the concomitant associations and consequences. When it comes to the scientific evidence of their effectiveness in accidents, there is clearly contradictory evidence: ecological, population-level studies showing no benefit, case-control studies showing benefits. So, naturally, I look to cyclehelmets.org to engage with the case-control studies to understand where they are going wrong. Instead of which, I find it basically says "they must be wrong so they are wrong", and it is rather selective on which studies (ie the ones that don't find risks) that it advances. So I increasingly conclude it is more of an advocacy site rather than a dispassionate information site - advocating a view I agree with, but advocacy nonetheless.

 

[swansonj]

PS @velovoice , my post above wasn't intended to be argumentative with yours, it was just that your mention of the site prompted me to say something that's been on my mind for a while.

 

[mjr]

Interesting statistic I came across while reading something else on Cheshire Police Twitter page:

Cheshire Police Retweeted
CheshPol taskforce ‏@CPTaskforce Oct 18


97% of fatally injured #cyclists died not wearing a #helmet. Give yourself a chance and #PutALidOnIt

One obvious strange thing is that there's no time or space boundaries on that claim, whereas cycle helmets are mostly modern, first-world and sports cycling, so it could well be true, as well as spectacularly uninformative.

Also, it says of fatally injured cyclists and not of fatal cycling injuries... so if I choke to death at the pub stop, does that still count as one of the 97%? Or what if I die in my sleep?

Hopefully, they'll answer on Twitter before someone uses www.WhatDoTheyKnow.com on them.

 

[Wobblers]

Whoa - hang on a tick - the Cheshire police stat of 97% is allegedly the % fatally injured cyclists not wearing a helmet. The TRT 85% figure is allegedly the reduction in fatal accidents caused by wearing a helmet. They are, of course, both probably wrong. But they are estimates of different quantities so surely can't be compared.

This is not the point I'm making. It is always a good idea to do some quick back of the envelope calculations to check whether the numbers seem reasonable. A sanity check, if you will. The Cheshire police number implies a 33 fold reduction in fatal injury in wearing a helmet. Or, considering a hypothetical population of 1000 cyclists of whom 100 have fatal accidents, 50% helmetted, the rest not, this 97% stat, to be consistent, must mean 97 of those weren't wearing helmets - that's a rate of 19.6% whilst the rate in the helmetted group is 0.6%. Which gives a 33 fold difference between groups. Of course, that differene becomes smaller as the nonhelmetted cohort increases. The rate is identical for both groups when the helmet wearers are 3% of the total cyclist population - and that's far below the actual percentage of those who wear helmets in the UK. (I am assuming that the accident rate per unit distance is identical for both cohorts.)

But even allowing for that, the TRT study reported less than a seven fold decrease - this is a very large discrepancy between the data. That alone ought to be enough to set alarm bells ringing. Were I, during the course of my work, to generate two data sets with such a large discrepancy between them, I'd immediately suspect both sets. In fact, I'd go back and check all the underlying assumptions and the model I was using - and check, if I could, by generating a third set of data by another way.

Here I've used the dataset that's already the most consistent with the Cheshire stat - a set we already know to be of dubious provenance. Even so, it still fails this most basic of sanity checks - badly. That can only lead to the conclusion that the 97% figure is very much suspect.

 

[Wobblers]

In which case, can i make the only mildly provocative comment that I increasingly don't think cyclehelmets.org is a reliable site.

I oppose helmets primarily for what you might call strategic and political reasons: that I don't think it serves the long-term interests of society or of the individuals that make it up to promote helmets with all the concomitant associations and consequences. When it comes to the scientific evidence of their effectiveness in accidents, there is clearly contradictory evidence: ecological, population-level studies showing no benefit, case-control studies showing benefits. So, naturally, I look to cyclehelmets.org to engage with the case-control studies to understand where they are going wrong. Instead of which, I find it basically says "they must be wrong so they are wrong", and it is rather selective on which studies (ie the ones that don't find risks) that it advances. So I increasingly conclude it is more of an advocacy site rather than a dispassionate information site - advocating a view I agree with, but advocacy nonetheless.

While I share your suspicion that cyclehelmets.org is reliable, there is also an issue with the reporting of negative results in the scientific literature. Put simply, a study that fails to show any positive benefit is less likely to get published - due largely to the fact that the researchers are less likely to seek to publish. In this context, that means that a study that fails to show a benefit to wearing helmets is less likely to end up in the literature. How many - if any - studies that show no benefits have never seen the light of day I have no idea. Which is the problem: we don't know the complete picture.