Espressopithecus (Java Man) wrote:
> Here's another study that contradicts your claim of consistency.
>
> http://pediatrics.aappublications.org/cgi/content/full/110/5/e60
The infamous McPherson study. Again the devil is in the detail.
45% drop in HI per 100,000 population but no measure of changes in
exposure (ie children cycling less).
Any child with any sort of HI was counted as a head injury, whether or
not that was the reason why they were hospitalised, so a scratch on the
face when they are in for a broken leg counts as a head injury. Looking
at injury rates (ie comparing changes in ratio of HI to other injury),
the protective effect was far less.
Surprisingly enough a helmet does provide protection against minor
injuries, and minor injuries are far more common than major ones. What
this study does not do is to separate minor from major, or even those
who were hospitalised because of HI vs those hospitalised for other
reasons.
So the study is flawed, the way the data is presented seems to be
intended to maximise the headline figures whilst minimising the amount
of useful information one can get from the study (it would be very
interesting to see what the spread of rates were from each province,
rather than lumping them all together. Why is this variation not shown?
And the final point is that of self selection and cross-sectional vs
longitudinal studies. This is a cross-sectional study. There is no
information on helmet wearing rates (several of the legislation
provinces have legislation but no enforcement, other provinces have no
legislation but de facto enforcement.
> It isn't my objective to prove that helmets are beneficial. My point
> has been, and remains, that none of the studies prove whether you or I
> would be safer or less safe if wearing a helmet while cycling.
I look at the biomechanics and evaluate that in the light of the whole
population studies.
My conclusions are:
1) cycle accidents are rare
2) cycle accidents where one hits ones head are even rarer.
3) helmets will work well for linear and minor abrasive impacts.
4) helmets do not prevent rotational impacts and may exacerbate them.
5) I am better off wearing a helmet in high incidence low impact
scenarios (e.g. XC MTB).
6) I am probably worse off wearing a helmet in low incidence high speed
scenarios (eg road)
> Those who say the studies "prove" that wearing a helmet while cycling
> reduces the risk of injury are, IMHO, as confused about the limitations
> of the data as those who say wearing a helmet increases the risk of
> injury. I don't think the data yet proves either proposition.
There is enough data to give plausible mechanisms both ways.
Understanding the limitations of the mechanisms is the key to
extrapolating them to real life.
...d