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Sep
16
2009

Seat belts again

Yesterday when I showed Mayer Hillman the graphs in my last blog on this subject he complained that they displayed the statistics for all road user deaths and not the statistics for those affected by the seatbelt law, i.e. people in the front seats of cars.

My excuse was that at the time I produced the graphs, almost 20 years ago, I was focused on total numbers because of the evidence that the law coincided, in Britain and elsewhere, with increases in the numbers of pedestrians and cyclists killed. Also, at that time no one was claiming that the law had saved anything remotely approaching the recent claim by the Government, RoSPA and PACTS of 2400 lives saved per year.

But stung by Mayer’s insistence that the claimed saving of 2400 lives per year was more than the total number of car occupants killed, I went back to the numbers.

The graph below shows the data for the same period for car occupants only. I asked the computer to fit a line to the data up to and including 1982 (the year before the law came into effect, small red arrow) and it produced the downward sloping trend displayed. When asked to fit a line to the statistics after the seatbelt law the computer replied with an upward trend. When the claimed 2400 lives saved is displayed on the graph it shows that the law should have brought impressive numbers back from the dead. The claim would appear to be based on the work of creationist statisticians.

picture-8Source: Road Accidents Great Britain: 1982 & 1989, Table 5,  HMSO.

6 comments

1 ping

  1. Dr. Robert Davis says:

    “and not the statistics for those affected by the seatbelt law, i.e. people in the front seats of cars.”

    Er… but the whole point is that pedestrians and cyclists WERE AFFECTED by the seat belt law, as you have shown. indeed, our culture has been profoundly adversely affected by a move which shifted risk from the more dangerous-to-others on to those less dangerous-to-others, and by using it as an exemplar of the way safety on the road should be addressed.

    Er… as I went on to note in the next sentence. JA

  2. Ben says:

    What is the relation between the number of car occupant deaths and the number of cars on the road or car journeys taken though, how does this impact the suggested trend?

    i.e. Was the increase from 82 to 90 due to increased car occupants, but the proportion of these that died actually decreased?

    A pertinent question. Traffic increased every year throughout this period except for 1974, the energy crisis year. But the increase was faster in the period after the seat belt law which probably accounts, at least in part, for the change of trend. The relationship between rate of change in traffic level and fatality rates is discussed in Risk and Freedom Chapter 7. JA

  3. Peter Gorman says:

    You are to be congratulated, sir, for your tireless exposure of the selfserving nonsense that passes for statistics in public debate.

  4. Guy Chapman says:

    In the BBC piece to which you refer, Philip Cowley asks why the seat belt law was accepted more readily than laws on, say, mobile phone use. If he honestly can’t see why this is then I can understand why he appears unable to accept the flaws in the statistics on seat belts. Wearing a seat belt does not prevent you from doing anything much and is there to protect you from bad drivers (i.e. /other/ drivers), whereas laws on drink-driving, speeding, phone use and so on are there to prevent bad drivers from being worse, and since you’re not a bad driver it surely can’t apply to you. I thought he was supposed to be a sociologist or something? This is pretty obvious stuff.

  5. Alex Goodlet says:

    Regarding the impact of seat belts on car occupant deaths it is quite clear that the 1982 law had little impact. What if a law had been passed in 1965 that all new cars should have seat belts fitted. Initially there would be only a few cars with seat belts and any impact would be swamped by the increased volume of vehicles. As the proportion of cars fitted with seat belts grew then any impact would become more significant. This would impact increase until all cars had seat belts.
    Car occupant deaths would then follow the increased volume of traffic. When all cars had seat belts it would then be a case of getting occupants to use them.

  6. Carsten Jasner says:

    Very interesting! But when the number of car occupant deaths increases while the number of all road user deaths decreases – how can the number of pedestrians and cyclists also increase?

    By the way: Do you know what the overall decline in traffic deaths over the years causes?

    ******************************************************************
    Carsten
    I have a go at answering your first question in a new blog.
    For my thoughts on your second question please see Chapter 7 of Risk and Freedom. JA

  1. velorution » Blog Archive » Doctors ignorami says:

    […] how compulsory helmet use will probably have no effect on the number of head injuries, just as the introduction of seat belts has had no impact on the reduction of road […]

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