The helmet section?

This sub-forum all discussions about this "lively" subject. All topics that are substantially about helmets will be moved here, if not placed here correctly in the first place.
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pjclinch
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Re: The helmet section?

Postby pjclinch » 29 Sep 2016, 9:54pm

Dave W wrote:Someone new puts up a statement that actually helmets do save lives, impossible can't be so can it?


Let's look a bit closer at what is being said and how.

First up, it's a statistical paper by statisticians. How come you've suddenly become a "stats believer"? Seems like a bit of a double standard... And it's not anyone new, it's Jake OIivier as lead author who's been a tireless denier of anything other than helmets being wonderful in Oz for a long time now.

Next, it's a meta-analysis, which means the authors have taken existing studies (i.e., it's not exactly new) and summarised their results. Which studies did they choose? They chose hospital admission case-control type studies, which suffer from numerous problems when applied to cycle helmets highlighted by statistician and risk specialist Prof. Sir David Spiegelhalter and epidemiologist Dr. Ben Goldacre in their British Medical Journal editorial in 2013. The authors of this study have done nothing to address the concerns raised there, and indeed have cherry-picked their studies to ignore the sort that find little or no benefit. That they include the likes of Thompson, Rivara and Thompson's shocker which compared helmet wearers typified by affluent families riding in parks to non-wearers typified by poor children riding on streets and, surprise surprise, found the former group did better than the latter, is just another indication that it's really an exercise in turd-polishing that totally fails to separate the choice from the chooser.

Pete.
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Dave W
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Re: The helmet section?

Postby Dave W » 29 Sep 2016, 10:21pm

Who said I was a stats believer? I put a link to another view that's all. When you've got people like GCN repeating the report what chance do you think you have?

Mike Sales
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Re: The helmet section?

Postby Mike Sales » 29 Sep 2016, 10:36pm

Dave W wrote:When you've got people like GCN repeating the report what chance do you think you have?


I guess you mean "Global Cycling Network"

Not any of these...
Global Compliance Network
Global Christian Network
Graphics Core Next
Gay Christian Network
Gay Community News
Global Communications Network

I have never heard of the Global Cycling Network.

I have heard of the British Medical Journal which published Spiegelhalter and Goldacre.

In any case, the current uncertainty about any benefits from helmet promotion or wearing is unlikely to be reduced by further research. Equally, we can be certain that helmets will continue to be debated, and at length. The enduring popularity of helmets as a proposed major intervention for increased road safety may lie not in their direct benefits- which seem too modest to capture compared with other strategies- but more with the cultural, psychological and political aspects of popular debate around risk.

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Re: The helmet section?

Postby Vorpal » 29 Sep 2016, 10:48pm

Dave W wrote:
Someone new puts up a statement that actually helmets do save lives, impossible can't be so can it?


On the thread linked above, where the discussion of the new study is, I noted that Rune Elvik did a similar meta study, only he found considerable bias in the published results.

What I didn't say on there, and something seldom discussed on this forum, is that Rune Elvik is cautiously in favour of helmet use. He suggests the promoting helmets to cyclists under 18 years old is cost effective. He has also stated that overall, helmets provide moderate benefit. He has done a couple of cost-benefit analysis for Norwegian road safety measures, in which he uses a 20% reduction in cyclist fatalities due to increased helmet use (for the purposes of cost-benefit analysis

Even though that is probably optimistic (It's still well down the list in terms of the benefit of road safety measures), you can from these things understand that Rune Elvik is by no means anti-helmet.

So, the point is that Rune Elvik is cautiously in favour of helmets, at least in some circumstances, yet when he did a meta-study similar to that done by Olivier, he found considerable bias in published studies and only a 'modest' benefit from wearing helmets. Furthermore, he found that modest benefit all but disappeared, looking only at recent studies.

Rune Elvik works at the Norwegian national transport research institute. Their page has some information about cycle helmets, that I think is fairly sensible (before you click, it's in Norwegian)
https://www.toi.no/forstesiden/riktig-i ... 497-4.html

You can stick it in a translator, but some things will probably not be completely clear, so I will tranlate, paraphrase & summarise:
-Helmets are useful for preventing injury in children
For adults...
-they are useful in reducing injury, given that an crash/incident has occurred
-cyclists who wear helmets take higher risk than those without
-so it is unclear whether helmets reduce the overall risk of injury
-it is also unclear whether legislation requiring helmets reduces the overall risk of injury
-studies that find large improvements in head injuries due to helmets usually have methodological issues, and are likey to overestimate the benefits
“In some ways, it is easier to be a dissident, for then one is without responsibility.”
― Nelson Mandela, Long Walk to Freedom

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pjclinch
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Re: The helmet section?

Postby pjclinch » 30 Sep 2016, 9:31am

Dave W wrote:Who said I was a stats believer? I put a link to another view that's all. When you've got people like GCN repeating the report what chance do you think you have?


I don't know what GCN is, but the fact it was in the Guardian is a pretty good indication that the PR battle is generally being won by the folk promoting this line of work.

But as both a cyclist and a science professional I'm not very interested in who's ahead at PR to underpin my choices, I'm interested in the quality of the work done. My confidence in Olivier's work, having looked at what he's up to, is very low. My confidence in cycle helmets as a life-saving measure is, having looked at their track record across populations, also very low. And I'll continue to say so as to just let helmet promotion take over has all the hallmarks of a public health own goal waiting to be scored.

Check out cycling in Olivier's home patch, and see where things can go... https://www.theguardian.com/commentisfree/2016/feb/27/hold-onto-your-helmets-here-comes-the-latest-anti-cycling-legislation

Again I'd like to emphasise that I have no problem with you and your pals choosing to wear them, and indeed given your accident rate that you appear happy to leave as it is I think it's probably a good idea. This isn't exactly an "anti helmet" view, which is where we came in, and it isn't "anti helmet" to avail people of what they can reasonably expect of helmets.

Pete.
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Re: The helmet section?

Postby Stevek76 » 30 Sep 2016, 12:28pm

Dave W wrote:It featured on the GCN cycling video on youtube.


Even for roadies they are exceptionally helmet keen, might be something to do with their sponsors :roll:

Still it's worth noting that GCN's core audience consists primarily of enthusiasts who follow pro racing etc. They (particularly the weekly show as opposed to the various how to vids) do not get watched by those who primarily use it as a form of transport, so I'm not sure them featuring it is much more than preaching to the converted.

Being in national papers like the guardian is likely to get a different audience though they did at least put out an editorial a couple of days later putting it into perspective a bit.

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Re: The helmet section?

Postby axel_knutt » 30 Sep 2016, 1:59pm

Dave W wrote:Exactly, I belong to two clubs, there are more in the area, accidents/crashes aren't particularly rare as I've tried to point out. Earlier this year another local came off when his seatpost snapped (hospital job) another slid off on diesel on his commute to work, another has smashed his shoulder offroad mountain biking and I was told of a second broken neck accident in Bristol the other day involving a car that pulled out again. I can probably think of twenty to thirty in the last two years within twenty miles of me some involving hospital treatment others not so bad. On top of that lot there are the racers, big crash at Thruxton a couple of months back which resulted in the chap getting airlifted to hospital plus all their group crashes. Two came back from the Newport Velodrome earlier this year with broken arms and legs.


https://en.wikipedia.org/wiki/Availability_heuristic
“I'm not upset that you lied to me, I'm upset that from now on I can't believe you.”
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Re: The helmet section?

Postby Dave W » 30 Sep 2016, 5:09pm

:lol:
image.png

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pjclinch
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Re: The helmet section?

Postby pjclinch » 30 Sep 2016, 7:32pm

It's not an insult to have sources of cognitive bias pointed out to you. You could try using it as useful information.
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Dave W
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Re: The helmet section?

Postby Dave W » 30 Sep 2016, 9:38pm

I don't need to thanks.


By the way what's in it for Olivier and Prudence Creighton do you think to publish this report?

I had a butchers of this report too http://www.trl.co.uk/news-hub/trl-press ... 4/july/trl’s-independent-review-of-compulsory-cycle-helmet-wearing-informs-jersey-scrutiny-panel/

Which seems at odds with your favourite report. How can so many clever people come to such ďifferent conclusions?

http://www.trl.co.uk/reports-publicatio ... ortid=6955

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Re: The helmet section?

Postby pjclinch » 30 Sep 2016, 10:09pm

Olivier et all think they're doing the world a favour. I think they're wrong.

The question at hand is, as Goldacre and Spiegelhalter pointed out, actually very tricky. It sounds quite simple, and as a consequnce there's no shortage of people that have underestimated it.

Quite a lot of pushing of stuff that doesn't really make the grade is down to cognitive bias. There's a lot of it about.

Pete.

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Re: The helmet section?

Postby Dave W » 30 Sep 2016, 10:21pm

Things like:
The effectiveness of helmets in the event of a collision
Although they cannot be expected to be protective in all collision types, the evidence is
clear that helmets are effective at reducing injuries:
• Helmets dramatically reduce head injury metrics in tests with crash dummy head-
forms and paediatric skulls.
• A large number of studies show that helmet wearers, if involved in a collision,
suffer fewer head injuries than un-helmeted cyclists.
When considering the situations in which helmets will be most effective it should be
noted that these tend to be the types of collision which are most common among cyclists
(non-vehicle collisions such as falls). It should also be noted that most studies focus on
the prevention of head injuries; there may be benefits associated with reducing the
severity of an injury, e.g. from severe to moderate, that are not accounted for in these
studies.
The impact of helmet legislation on injuries
The evidence as a whole suggests that mandatory cycle helmet legislation is associated
with a reduction in reported head injuries

There's about 54 pages in that report so not light reading but very different to Goldacre and Uk based I believe?

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Re: The helmet section?

Postby roubaixtuesday » 30 Sep 2016, 10:37pm

How can so many clever people come to such ďifferent


This is a very good question Dave W.

You could ask yourself how any answer to it might inform your apparent very strong views on the advisability of wearing a helmet.

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Re: The helmet section?

Postby Vorpal » 30 Sep 2016, 10:53pm

Dave W wrote:How can so many clever people come to such ďiferent conclusions?


First of all, most of the bicycle helmets studies that show benefit are hospital case studies. The biggest problem with that, of course is that they've ended up in the hospital. As you rightly pointed out, we need to look at the folks who didn't land in hospital, as well.

In theory, they should be able to compare the folks in the hospital with any random population of cyclists.

In practice, this all but impossible. Where do you get the random sample? And how do you know whether they wear helmets? Are any of them already included in the population that have been hospitalized?

Next, you have problem of *which* hospital cases to include. Including those who were admitted with broken collar bones won't tell you much about whether a helmet was useful, even if you can find out whether they were wearing them. Different studies include / or exclude different hospital cases. While the reasoning has to be justified, the results can be very different. In the case of meta-analyses, they have to decide which previous analysis they include. In the case of Olivier et al, they included one study which found a large benefit (85%) in wearing a helmet, but that study has been rightly criticised, and even the original authors agree that there were basic methodological problems with the study.

Lastly, you have the statistics used to analysed the data. Besides the pure analysis of how many people end up in each set and what percentage had/didn't have head injuries, there are typically other factors that have to be included or accounted for. Among them are things like whether the population is representative, and whether it is possible to correct for differences.

Most fields are subject to publication bias, and some also have problems with other biases. Time trends, medical capability, and other things can influence the data, so most researchers attempt to correct for these.

They also use things like odds ratios and confidence intervals to estimate how wrong they might be. How these are used and calculated can also vary from one study to another. Odds ratios are a weighted estimate using the log mean of individual estimates. A good study will test the methods by using and comparing alternatives.
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Re: The helmet section?

Postby axel_knutt » 1 Oct 2016, 11:12am

pjclinch wrote:the PR battle is generally being won ..............I'm not very interested in who's ahead at PR to underpin my choices

Once the PR battle has been won you won't have any choice.
“I'm not upset that you lied to me, I'm upset that from now on I can't believe you.”
― Friedrich Nietzsche