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Sep
03
2009

Seat belts – myth inflation update

The myth of the efficacy of seat belts laws has become deeply embedded. Their “success” is routinely invoked in all sorts of unrelated arguments: e.g. “Opposing wind farms is as ‘socially unacceptable’ as not wearing a seatbelt” says the climate change minister.

Every so often it is given a boost by an outrageous claim that goes unchallenged and gets widely reported. Or if challenged, the challenge goes unacknowledged and unreported – see my post Myth Inflation on the DfT claim that the UK seat belt law has saved 60000 lives in the last 25 years..

The issue has come to my attention again at this time because I am preparing for a debate hosted by the College of Emergency Medicine on the resolution ”This house believes that helmets should be mandatory for all cycling children” and the proposer, Andrew Curran cites the success of seat belt laws (without citing any evidence) as an argument for the compulsory wearing of helmets.

But also because the myth has just been given an enormous boost by another widely reported whopper. “The man who saved a million lives: Nils Bohlin – inventor of the seatbelt.” This headline on 19 August in The Independent was repeated with minor variations in thousands of headlines and websites all round the world.

The number comes from a Volvo press release that says “Estimates put the figure at just over a million lives.” And it comes with a footnote: “Estimate by Volvo based on general and in-house statistics on accidents and belt use.”

On 17 August I sent them an email: “In your press release ‘A MILLION LIVES SAVED SINCE VOLVO INVENTED THE THREE-POINT SAFETY BELT’ at http://www.volvocars.com/uk/footer/about/NewsEvents/News/Pages/default.aspx?item=190 the source of the million estimate given in footnote 4 is ‘Estimate by Volvo based on general and in-house statistics on accidents and belt use’. I don’t like to use a number without knowing how it was produced. I would be grateful if you would provide the method by which it was produced and the statistics upon which it is based.”

On 2 September I received this reply:

“Unfortunately it’s very difficult to put an exact figure on the number of lives the three-point safety belt has saved since 1959 as there are no globally coordinated traffic safety statistics. The million number is an estimation based on numbers provided by a number of government departments around the world and Volvo’s in-house statistics on accidents and belt use.”

To which I replied:

“Thank you for your reply.

Some estimations are more accurate than others. If statistics are scarce (and in this case I agree that they are) the estimation is likely to be less accurate. But for it to be an “estimation”, as distinct from a wild-off-the-top-of-the-head guess, it must be based on a method and fed with some numbers.

Can you tell me the method used and the numbers with which it was fed? If not I must conclude that it is a self-interested wild-off-the-top-of-the-head guess. An indication of my reasons for doubting your “estimation” can be found on my website – http://john-adams.co.uk/2008/01/31/myth-inflation/.”

Correspondence was closed the same day:

Thank you for your reply. I’m afraid I can’t offer any further information other than what’s detailed below (i.e. previous answer). I appreciate your concerns and I apologise that I can’t offer any further assistance.”

I suspect that opposing wind farms probably is as socially unacceptable as not wearing a seat belt, but that is a grammatically elliptical discussion for another day.


Bicycle helmets — does the dental profession have a role in promoting their use? British Dental Journal 196, 555 – 560 (2004 ) H R Chapman & A L M Curran

2 comments

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  1. Jim Tubman says:

    Good luck with the cycle helmet debate. Let us know how it turns out.

    As you may know, a cycle helmet law for children was passed in the Canadian province of Alberta in 2002. Within 6 months, the head injury rate for child cyclists appeared to have doubled:

    http://www.vehicularcyclist.com/CalgarySun.htm

    Some of that may be an artifact of a change to the system of injury recording. But it is telling that there is no sign that any follow-up work was done to investigate this finding, or to track any benefit from this law. Instead, subsequent monitoring of the effects of the law appears to have focused on measuring compliance only.

    One has to wonder whether it is simply assumed that compliance leads to actual improvements in safety, or whether changing the definition of success to compliance is an attempt to deflect attention away from a failed policy.

  2. Piet de Jong says:

    I don’t know how many lives have been saved by seat belt laws. I doubt anyone does. Many people claim that “many” have been saved. And that this “fact” justifies the law.

    Instead of arguing about how many lives have actually been saved, perhaps a more constructive way forward would be to establish the threshold number of lives saved that would justify the law. And once the threshold has been agreed upon to then establish not the actual number saved, but whether it is plausible that the actual number exceeds the threshold. This is simpler statistical exercise than determining the actual number saved. I would be surprised if a reasonably determined threshold has not been exceeded.

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