[SystemSafety] Bicycle Helmets

[DREW Rae]

>Fuzziness of the data notwithstanding, if we agree that helmets provide
say '-x' degree of risk reduction, but in the two populations the
proportion of injuries is still roughly the same, then we >could conclude
there must be some source of additional risk equal to 'x' that helmeted
riders are exposed to? If so what is that risk? Or am I missing something?
>
>Matthew Squair

That's the thing. The data _don't_ show that in the two populations the
proportion of injuries is still roughly the same. The studies reasonably
consistently show that for the same group of people cycling, wearing a
helmet reduces the proportion of serious head injuries. The only studies
that show differently are looking at different populations through some
form of systematic measurement  error which is obvious from the way the
study is reported. The main examples are:
 - reporting bias excluding the population who have helmet + no serious
injury (e.g. by counting at the point of hospital admission)
 - population skew by measuring before and after a helmet law, where the
makeup of the cycling population changes before and after

I'm not sure there's anyone on the list trying to make the claim that the
proportion of injuries is the same in equal populations. Peter gave one
paper to provoke discussion, but as I understand he agrees that it has a
systematic sampling problem.

I should also pre-empt another problem that hasn't come up in the
discussion yet - the evidence is very mixed for facial injuries rather than
head injuries. The mechanism of injury is quite different, and there are
plausible ways a helmet without a faceplate can increase as well as
decrease scratching and bruising to the face.

A couple of people also pointed to the "paper" where a guy stuck a video
camera on the back of his bike and claimed that wearing a helmet caused
more dangerous driver behaviour around the cyclist. Full points for
initiative, major deductions for rigour, statistical methods questionable,
and not supported by the other evidence.

Drew

My safety podcast: disastercast.co.uk
My mobile (until October 2nd): +44 7783 446 814
My mobile (from October 6th): 0450 161 361

On Thu, Oct 16, 2014 at 6:44 AM, Mike Ellims <michael.ellims at tesco.net>
wrote:

> I suspect that this  boils down to a few simple things;
>
>
>
> Helmets are designed to absorb a certain amount of energy, once it’s done
> doing that it can’t absorb any more and the impact is delivered directly
> though to the head. Kinetic energy being what it is, once the speeds go
> beyond a critical threshold wearing a helmet doesn’t make any significant
> difference;  1/2mv^2 rules – whether you like it or not.
>
>
>
> It also depends on what you hit, hitting a flattish surface is better than
> hitting something with a hard edge such as the  curb.
>
>
>
> It also depends on the sequence of events  i.e. hitting headfirst is not
> good, but hitting with a shoulder will absorb much of the initial impact.
> It also helps if you slide as energy is dissipated over a longer period of
> time.
>
>
>
> Bike helmets are much like cars which are designed for the most
> statistically common accident, i.e. frontal impacts at 50 kph and side
> impacts at around 18 kph. This doesn’t mean the car will protect you in a
> collision at 150 kph (1/2mv^2 again).
>
>
>
>
>
> *From:* systemsafety-bounces at lists.techfak.uni-bielefeld.de [mailto:
> systemsafety-bounces at lists.techfak.uni-bielefeld.de] *On Behalf Of *Matthew
> Squair
> *Sent:* 15 October 2014 20:30
> *To:* Peter Bernard Ladkin
> *Cc:* systemsafety at lists.techfak.uni-bielefeld.de
> *Subject:* Re: [SystemSafety] Bicycle Helmets
>
>
>
> Likewise I have a bicyclist friend who was hit by a car and her helmet
> saved her from severe brain trauma.
>
>
>
> This was her second bad concussion from riding within the space of a
> couple of months, and as we found out the only thing the brain likes less
> than being shaken vigorously is having it done again.
>
>
>
> Fuzziness of the data notwithstanding, if we agree that helmets provide
> say '-x' degree of risk reduction, but in the two populations the
> proportion of injuries is still roughly the same, then we could conclude
> there must be some source of additional risk equal to 'x' that helmeted
> riders are exposed to? If so what is that risk? Or am I missing something?
>
>
> Matthew Squair
>
>
>
> MIEAust, CPEng
>
> Mob: +61 488770655
>
> Email; Mattsquair at gmail.com
>
> Web: http://criticaluncertainties.com
>
>
> On 15 Oct 2014, at 6:52 am, Peter Bernard Ladkin <
> ladkin at rvs.uni-bielefeld.de> wrote:
>
>
>
> On 2014-10-15 00:01 , David Crocker wrote:
>
> I have some indirect experience of the value of cycle helmets.
>
>
> David's story is similar to what happened in one of the two incidents to
> my friend who wrecked two
> helmets and her jaw, but in her case it was a lamppost base.
>
> That's the puzzle. The value of helmets is obvious - many of us seem to
> know some one or more whose
> lives have been saved - but apparently not from the numbers.
>
> PBL
>
> Prof. Peter Bernard Ladkin, Faculty of Technology, University of
> Bielefeld, 33594 Bielefeld, Germany
> Tel+msg +49 (0)521 880 7319  www.rvs.uni-bielefeld.de
>
>
>
>
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