The CycleChat Helmet Debate Thread

[Tin Pot]

The headline has rounded up the figure in the article from 65%, and doesn't say how they aggregated the 40 studies to get these figures which is a shame - I'm all for more information and science on this, but it need some to be solid. This seems a little murky.

But either way a $319 fine is outrageous, and makes me suspicious.

 

[srw]

Small details are however still quite important.

Not if you want to understand something scientifically.

 

[Fab Foodie]

Does Oxford really buck the national trend and have most people wearing helmets?

Guess it's time I switched my allegiance to the light blues, then. They aren't as irrational!

Well there's not a lot of helmet wearing from what I see ... Apart from the Mamils.

 

[Profpointy]

Radius does take account of this, because a round thing, like a head in a helmet, doesn't have just one radius in one direction. It's the thickness of the helmet, and therefore the direction the head has to travel to make impact in whichever direction you happen to be falling today which makes the difference.

If it was the chance of a raindrop landing on your helmet, then it would be horizontal cross section. If it was the chance of a low flying bird hitting it as it flew past, then it's the height of the helmet that matters. I think falling and hitting your head is more like the second example.

Your bird strike assessment is flat out wrong The helmet is higher and wider so it's the greater area in the direction of the bird which matters.

I suggest that falling off a bike onto the floor is similar. If it was purely width (radius) then you could simply wear polystyrene ear muffs rather than a helmet proper

 

[winjim]

Click on the abstract and, unless I've seriously misunderstood something, that's not what the research actually says. In other words, the press release on which the article is based is lying.

It talks about an odds reduction in any kind of head injury of about 50%, of a serious head injury somewhere between 25% and 40%, of a face injury of about 70% (actually between 56% and 80%) and of a fatal head injury of somewhere between 15% and 90%.

http://ije.oxfordjournals.org/content/early/2016/09/06/ije.dyw153.abstract

Someone with access to the article itself can, I'm sure, point out more flaws.

They've used 1-OR.

So if the odds ratio is 0.37, then the odds reduction is 0.63.

 

[mjr]

It's not a study - it's a review of existing studies. And your choice of which studies you include in your review will impact the outcome. If it contains anything by Thomson and Rivara you'll know it's a crap review...

I've seen a claim that it does. Both the 1989 and 1996 studies.

It's being dismantled over at http://forum.cyclinguk.org/viewtopic.php?f=41&t=109262 by cleverer people than me with more time than me today.

 

[hatless]

Your bird strike assessment is flat out wrong The helmet is higher and wider so it's the greater area in the direction of the bird which matters.

I suggest that falling off a bike onto the floor is similar. If it was purely width (radius) then you could simply wear polystyrene ear muffs rather than a helmet proper

If you picture a bird with its wings outstretched (which is what I had in mind), then it's the height of the helmeted head that matters. Width would be an issue in hitting a wasp, but not a flat thing like a wide bird or a subway roof.

Polystyrene ear muffs would have an identical effect to a helmet as long as you fell so that they were between you and the thing you hit. If you wore them on forehead and occiput rather than ears, then you could land face down or face up. That would still be radius, which is length as well as width.

 

[Profpointy]

If you picture a bird with its wings outstretched (which is what I had in mind), then it's the height of the helmeted head that matters. Width would be an issue in hitting a wasp, but not a flat thing like a wide bird or a subway roof.

Polystyrene ear muffs would have an identical effect to a helmet as long as you fell so that they were between you and the thing you hit. If you wore them on forehead and occiput rather than ears, then you could land face down or face up. That would still be radius, which is length as well as width.

Your explanation is quite right -but you seem to be conculding it's lenght not area - which is quite wrong from your own explanarion

.... unless I've misenderstood and we're actually violently agreeing

 

[Fab Foodie]

Oh goody .... am going to be told about this numerous times during tonight's club run .....

 

[srw]

Oh goody .... am going to be told about this numerous times during tonight's club run .....

http://forum.cyclinguk.org/viewtopic.php?f=41&t=109262#p1052328

Point out that Goldacre and Spiegelhalter, the UK's pre-eminent experts in this sort of thing, managed to refute the conclusions of the paper in the BMJ a couple of years before it was published.

 

[Fab Foodie]

http://forum.cyclinguk.org/viewtopic.php?f=41&t=109262#p1052328

Point out that Goldacre and Spiegelhalter, the UK's pre-eminent experts in this sort of thing, managed to refute the conclusions of the paper in the BMJ a couple of years before it was published.

My hero!

 

[Wobblers]

Radius does take account of this, because a round thing, like a head in a helmet, doesn't have just one radius in one direction. It's the thickness of the helmet, and therefore the direction the head has to travel to make impact in whichever direction you happen to be falling today which makes the difference.

If it was the chance of a raindrop landing on your helmet, then it would be horizontal cross section. If it was the chance of a low flying bird hitting it as it flew past, then it's the height of the helmet that matters. I think falling and hitting your head is more like the second example.

Wrong.

This would only be true if you - and every cyclist - hit their heads in exactly the same angle, every single time. Except of course, this is untrue. You can fall off and hit any part of your head, at any angle. This is obvious, is it not? You need to stop thinking about just one instance, which (say) someone strikes their head at an angle of 58 degrees to the anterior and consider another accident, where the angle is 42 degrees, and the next, and the next. Take one thousand instances and you'll approach the full 360 degrees. You cannot predict which angle impact will happen. Hence the requirement to model impact probability with area. Which, again rather obviously, is why helmets are round(ish).

 

[glasgowcyclist]

Bicycle helmets reduce risk of serious head injury by nearly 70%, study finds - the guardian
https://apple.news/AucO_w6tKRgKTfCBk4mM2Pw

There's an interesting analysis of that study here:

http://www.treehugger.com/bikes/new...ce-risk-serious-injury-nearly-70-percent.html

"That makes sense. Helmets do prevent injuries and save lives. That's why we have to wear them on construction sites which are dangerous places where things fall on your head. But so far as I can tell, the study doesn't look at the rate of accidents, which surely matters. This is what risk means, and according to Kay Teschke of the School of Population and Public Health, University of British Columbia, who tweeted me a note:

The authors of the study seem to be very careful not to use that word, because they did not study risk. Their review is about the odds of a head injury given [a cyclist has an] injury. The studies take place at hospitals and they count the cyclists with head injuries wearing or not wearing a helmet and compare them to those with other injuries wearing or not wearing a helmet. The evidence on this issue is not contentious, helmets reduce the odds of a head injury among those who are injured when cycling (and would do the same for walking, car driving, etc. as many people have pointed out). "​

GC

 

[Tin Pot]

There's an interesting analysis of that study here:

http://www.treehugger.com/bikes/new...ce-risk-serious-injury-nearly-70-percent.html

"That makes sense. Helmets do prevent injuries and save lives. That's why we have to wear them on construction sites which are dangerous places where things fall on your head. But so far as I can tell, the study doesn't look at the rate of accidents, which surely matters. This is what risk means, and according to Kay Teschke of the School of Population and Public Health, University of British Columbia, who tweeted me a note:

The authors of the study seem to be very careful not to use that word, because they did not study risk. Their review is about the odds of a head injury given [a cyclist has an] injury. The studies take place at hospitals and they count the cyclists with head injuries wearing or not wearing a helmet and compare them to those with other injuries wearing or not wearing a helmet. The evidence on this issue is not contentious, helmets reduce the odds of a head injury among those who are injured when cycling (and would do the same for walking, car driving, etc. as many people have pointed out). "​

GC

I understand the point, but it's not really a criticism of the study; I am (amongst other things) a risk professional - I agree with the point which is that you must have probability and impact to be talking about risk.

The study is looking at probability, but within the incidence of injury - not the overall risk of injury.

 

[srw]

There's an interesting analysis of that study here:

http://www.treehugger.com/bikes/new...ce-risk-serious-injury-nearly-70-percent.html

"That makes sense. Helmets do prevent injuries and save lives. That's why we have to wear them on construction sites which are dangerous places where things fall on your head. But so far as I can tell, the study doesn't look at the rate of accidents, which surely matters. This is what risk means, and according to Kay Teschke of the School of Population and Public Health, University of British Columbia, who tweeted me a note:

The authors of the study seem to be very careful not to use that word, because they did not study risk. Their review is about the odds of a head injury given [a cyclist has an] injury. The studies take place at hospitals and they count the cyclists with head injuries wearing or not wearing a helmet and compare them to those with other injuries wearing or not wearing a helmet. The evidence on this issue is not contentious, helmets reduce the odds of a head injury among those who are injured when cycling (and would do the same for walking, car driving, etc. as many people have pointed out). "​

GC

Where do I start?

Risk doesn't mean the rate of accidents, it's a combination of the rate and the severity. As the URL indicates, the word "risk" appears large in the reporting of the study (press release probably prepared by the authors' institution). The review isn't about the odds of a head injury given injury, it's about the odds of a head injury given admission to hospital. Mathematically and in other ways it's plausible that helmet wearers are more likely to turn up in hospital, but once there are less likely to have a particular kind of injury. The evidence on the question of whether helmets reduce the odds of a head injury is still contentious.

Based on that series of errors I'm not going to click on the link.