Tuesday, September 18, 2007

Helmets..How safe is it?

1. Helmets are shown to have no statistically significant effect on the probability of a
fatality given that a motorcycle accident has occurred. This means that based on standard
statistical tests we cannot reject the claim that helmets do not affect the probability that a
rider will survive a motorcycle accident.
2. The major determinants of fatality are the rider's crash speed (kinetic energy) and
blood alcohol level.
3. For the average rider involved in the average accident, it is found that the probability
of death increases from 2.1% to 11.3% when the rider's blood alcohol level increases
from 0.0 to 0.1 (from sober to legally intoxicated in most states).
4. In the same vein, an increase in the crash speed from 40 to 60 mph increases the
probability of death from 7.1% to 36.3%
5. It is found that helmets have a statistically significant effect in reducing head injury
severity. We can reject the hypothesis that helmets have no effect on head injuries in
favor of the claim that they reduce head injuries.

6. It is shown that past a critical impact velocity to the helmet (approximately 13 mph),
helmet use has a statistically significant effect which increases the severity of neck
injuries. Thus we reject the claim that, helmets have no effect on neck injuries in favor of
the claim that, past a critical impact speed, they exacerbate neck injuries.
7. As a result of (5) and (6), we establish that a tradeoff between head and neck
injuries confronts a potential helmet user. Past a critical impact speed to the helmet
(13 mph), which is likely to occur in real life accident situations helmet use reduces
the severity of head injuries at the expense of increasing the severity of neck
injuries."
So helmets are proven in this report, to significantly reduce head iunjuries. It also reports that above 13mph the helmet "exacerbates" neck injuries. That does not mean helmets cause neck injuries, but they can exacerbate neck injuries. That in itself is not substantial arguement against wearing helmets, but also is not substantial arguement to fight mandatory helmet laws.
Keep in mind the 13 mph speed has little to do with the cycle speed at the time of the accident. That speed is the actual speed of the rider's body in motion when the helmet worn struck something. A rider could fall off a bike at 45 mph, and slide some distance (scrubbing off speed, literally) before striking an object at a speed close to the 13 mph mentioned in the report.

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