From: Derek C on
On 17 May, 10:08, Peter Clinch <p.j.cli...(a)> wrote:
> Derek C wrote:
> > Well I have to say (touch wood) that I have never slipped and banged
> > my head on a hard surface in the bathroom yet, but I have injured
> > myself several times in bicycle accidents, including a fractured upper
> > jaw bone when I bit a very hard kerbstone. I have fallen downstairs
> > once, when my dog came bounding up the stairs just as I was starting
> > down them and I tripped over him. I fell onto a nice soft carpetted
> > floor in the hallway and my only injury was a small broken bone in my
> > wrist. Perhaps we should ban dogs in the home?
> What the above shows is you don't properly appreciate one of the
> fundamental thinsg about risk, chance and probability, which is the
> degree to which a past event will influence a future one.
> If I roll a pair of fair dice 10 times and roll no 7s then it doesn't
> alter the fact that on the 11th roll I'm more likely to get a 7 than
> anything else.  Your odds of a bathroom accident are still very much
> finite and tangible.
> Beyond that, most bike helmets don't protect jaws that well, so I take
> it you've invested in a full-face one to reflect your past experience?
> Pete.
> --
There is also a small probability that the same lottery numbers could
come up two weeks running. What does that prove?

Derek C
From: Peter Clinch on
Derek C wrote:

> There is also a small probability that the same lottery numbers could
> come up two weeks running. What does that prove?

It proves that people thinking the last draws should be studied to
choose their next strategy are in the dark about probability.

But you seem to be using your past draws in the accident lottery to plan
your head protection strategy. The key is to use /everyone's/ past
draws to assess the actual risk, unless your cycling habits are such
that they give you an outsize chance of being in an accident.

Peter Clinch Medical Physics IT Officer
Tel 44 1382 660111 ext. 33637 Univ. of Dundee, Ninewells Hospital
Fax 44 1382 640177 Dundee DD1 9SY Scotland UK
net p.j.clinch(a)
From: Mike Clark on
In message <858dboF3kmU1(a)>
Peter Clinch <p.j.clinch(a)> wrote:

> Derek C wrote:
> > I feel far from bomb proof when riding a bike, with or without a
> > helmet, especially when being continuously overtaken by a stream of
> > fast moving (by bicycle standards) cars and lorries. I am certainly
> > not prepared to take any more risks just because I am wearing a
> > helmet!
> It's not entirely unheard of for people to refuse to go out without
> a helmet. So if they're going at all into what they perceive is a
> risky environment then they're taking greater risks because if they
> didn't wear the helmet, they wouldn't be in what they think is the
> risky environment.
> It's not about feeling invulnerable, it's about being there at all.
> Pete.

Precisely it's not that all people modify their behaviour to the same
extent or even in the same direction, and within a population the
average change might be small.

But it is also quite clear that some people modify their behaviour in a
radical way i.e. by making a decision that the risks of cycling are only
made acceptable by wearing a helmet.

The perceived difference that the helmet makes to their safety becomes a
deciding factor in whether or not they are prepared to cycle at all. JMS
would appear to be someone who is only prepared to accept the risks of
cycling as modified by the wearing of a helmet.

What I find incredible is that these same people who wouldn't be
prepared to cycle without wearing a helmet because they perceive the
risks to be too great, then claim that it couldn't possibly modify
others behaviour in different ways.

o/ \\ // |\ ,_ o Mike Clark
<\__,\\ // __o | \ / /\, "A mountain climbing, cycling, skiing,
"> || _`\<,_ |__\ \> | caving, antibody engineer and
` || (_)/ (_) | \corn computer user"
From: Tony Raven on
Derek C wrote:
> --
> Read some of the abstracts in TRL PPR446, available on-line as a free
> download, although �45 to buy. The most conservative estimate is that
> 10-16% of cycling fatalities would have been prevented by wearing
> helmets. Some American studies claim up to an 85% reduction.

Some claim up to 85%? I think you mean one does. Would you care to
describe the characteristics of the two cohorts used in that study and
why you think confounding factors did not apply given their significant

TRL's estimates above are totally predicated on two assumptions the
authors plucked out of the air. One is that "The effectiveness of cycle
helmets in single-vehicle collisions was estimated to be 50%." and the
other is the counterpart 10-30% estimate in multi-vehicle collisions.
There is nothing to justify those assumptions and indeed the authors
themselves admit it when they say

"Overall, it is concluded that it is not possible to determine
definitively from the literature the level of effectiveness of cycle

So we are left with nothing more than "we guessed".

Of course if you start off assuming they are effective you will conclude
they are effective. If they had started off assuming there was no
effectiveness they would have concluded 0% of cycling fatalities would
have been prevented. So their 10-16% conclusion is meaningless and
typical of much of the poor science that infects this field.


" I would never die for my beliefs because I might be wrong."
Bertrand Russell
From: Mike Clark on
In message <bb0f5a15-4ac1-4e0d-85c1-008c9ddcb48a(a)>
Derek C <del.copeland(a)> wrote:

> Safety in the home and the bathroom, and safety on bicycles are two
> completely separate issues. We are all going to die eventually, so why
> bother to take any sensible precautions at all? Let's do away with
> Health & Safety legislation, seat belts, airbags and crumple zones in
> vehicles, speed limits, motorcycle helmets, clean drinking water,
> sanitation, etc, etc. On the other hand it is nice to get your three
> score years and ten on this planet, and not to get disabled or brain
> damaged on the way.

But the irony is that cyclists, regardless of whether they wear a helmet
or not, are more likely than non-cyclists to get in their three score
years and ten, and with a good quality of life. It's not the wearing of
the helmet that does that, it's the physical activity.

o/ \\ // |\ ,_ o Mike Clark
<\__,\\ // __o | \ / /\, "A mountain climbing, cycling, skiing,
"> || _`\<,_ |__\ \> | caving, antibody engineer and
` || (_)/ (_) | \corn computer user"