From: marc@tanda.isis.org (Marc Thibault)
Reply-To: marc@tanda.isis.org
Newsgroups: ont.general
Subject: Risks and Bicycle Helmets
Date: Thu, 13 Aug 92 16:55:04 EDT
Distribution: na
Organization: Thibault & Friends


        Terry Jones has challenged my post regarding the small
        incremental benefit of wearing a bicycle helmet (and well he
        should, but he didn't offer better numbers). The following is
        an edited version of my reply to Terry.

        Since facts are eversomore interesting than anecdotes about
        what happened to somebody's brother-in-law's dog's previous
        owner, I'm presenting my WAG for examination and, hopefully,
        improvement. With all of the people on the net, we should be
        able to get better-derived numbers and a true picture of the
        risks. I hate to be a spoil-sport, and mess up this marvellous
        game of "ain't it awful" but how about it? Does anybody out
        there have real data to contribute?

        1) I remember somebody saying that there are about 270,000
        "frequent" cyclists in Ontario (whatever that means).

        2) There were 29 cycle-related deaths in Ontario last year.
        Let's be conservative and assume that they were all cranial
        injuries to people who were not wearing helmets and that (as
        MOT claims) 75% of them would have been prevented if the
        people had worn helmets. This is very generously in favor of
        the pro-helmet case. It is much more likely that the actual
        number was lower.

        3) Lets assume one trip per week in good weather, ie. 20. Once
        again this is very generous. "Frequent" cyclers probably
        average much higher numbers than that.

        The rest is simple arithmetic:

            a:  Number of cycle deaths last year       29
            b:  Number of frequent cyclists       270,000
            c:  Annualized risk (a/b)             1.1E-04
            d:  Average trips annually                 20
            e:  Per-trip risk   (c/d)             5.4E-06
            f:  Per-trip risk with helmet (e/4)   1.4E-06

        Because of the conservative choice of numbers, this is a high
        estimate. But even if I was out by a few orders of magnitude,
        the point remains that the incremental benefit of wearing a
        bicycle helmet is vanishingly small.

        What happens in these situations is that when attention
        focuses on a particular activity, all the anecdotes come
        flying out of the woodwork and the perception of risk gets
        blown way out of proportion to the actual risk. My personal
        anecdote is that I personally don't know anyone who has been
        seriously injured on a bicycle (or motorcycle), but I know two
        people who won lotteries and one who was struck by lightning.

        Last year somebody published a table of the risks of various
        activities. What I remember is that the thing one really
        should avoid is sport fishing in Northern Ontario. This is
        vastly more dangerous than cycling without a helmet!

        It would be nice, of course, if somebody could come up with
        good numbers not only for deaths but for injuries by type and
        estimates of total trips and/or miles for the whole
        population, preferably segmented to distinguish commuting, club,
        professional and competition riders from the population at
        large. Segmentation by age would be nice too. (When pigs fly!
        We've been trying unsuccessfully to get useful numbers about
        motorcycles for years, and they are all licensed; person and
        machine, so all the data we need are in various peoples'
        computers.)

                ,Marc




--
 Marc Thibault        |                              |  Any Warming,
 marc@tanda.isis.org  |  Oxford Mills, Ontario       |  Global or otherwise,
 CIS:71441,2226       |     Canada                   |   appreciated.

Xref: sparky ont.general:1573 can.general:3992 soc.culture.canada:5747 ott.general:839