February 15, 2013

There oughtta be a law

David Farrar (among others) has written about a recent Coroner’s recommendation that high-visibility clothing should be compulsory for cyclists.  As he notes, ” if you are cycling at night you are a special sort of moron if you do not wear hi-vis gear”, but he rightly points out that isn’t the whole issue.

It’s easy to analyse a proposed law as if the only changes that result are those the law intends: everyone will cycle the same way, but they will all be wearing lurid chartreuse studded with flashing lights and will live happily ever after.  But safety laws, like other public-health interventions, need to be assessed on what will actually happen.

Bicycle helmet laws are a standard example.  There is overwhelming evidence that wearing a bicycle helmet reduces the risk of brain injury, but there’s also pretty good evidence that requiring bicycle helmets reduces cycling. Reducing the number of cyclists is bad from an individual-health point of view and also makes cycling less safe for those who remain. It’s not obvious how to optimise this tradeoff, but my guess based on no evidence is that pro-helmet propaganda might be better than helmet laws.

Another example was a proposal by some US airlines to require small children to have their own seat rather than flying in a parent’s lap. It’s clear that having their own seat is safer, but also much more expensive.  If any noticeable fraction of these families ended up driving rather than flying because of the extra cost, the extra deaths on the road would far outweigh those saved in the air.

It’s hard to predict the exact side-effects of a law, but that doesn’t mean they can be ignored any more than the exact side-effects of new medications can be ignored. The problem is that no-one will admit they don’t know the effects of a proposed law.  It took us decades to persuade physicians that they don’t magically know the effects of new treatments; let’s hope it doesn’t take much longer in the policy world.

[PS: yes, I do wear a helmet when cycling, except in the Netherlands, where bikes rule]


Thomas Lumley (@tslumley) is Professor of Biostatistics at the University of Auckland. His research interests include semiparametric models, survey sampling, statistical computing, foundations of statistics, and whatever methodological problems his medical collaborators come up with. He also blogs at Biased and Inefficient

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  • avatar
    Nick Iversen

    New article out this week: Effects of Bicycle Helmet Laws on Children’s Injuries (http://www.nber.org/papers/w18773) which gives further side effects of the laws.

    Helmet “laws also are associated with decreases in non-head cycling injuries, as well as increases in head injuries from other wheeled sports.”

    It appears that if kids aren’t allowed to injure their heads on bicycles they move to skateboarding, roller skates and scooters to get their injury dose.

    5 years ago

  • avatar
    David Welch

    “ if you are cycling at night you are a special sort of moron if you do not wear hi-vis gear”

    I hope you aren’t condoning that unjustified slur.

    One of the stranger things about the coroner’s recommendation was that the poor guy who got killer was actually wearing fluoro gear. Didn’t really help in that case.

    5 years ago

    • avatar
      Thomas Lumley


      I wouldn’t have chosen those words, but I do endorse the advice. But if the guy who got killed was wearing fluoro gear it’s hardly an insult to him.

      5 years ago

  • avatar

    Way to blame the victim. Perhaps it takes a special type of moron to have two (or more) extremely powerful 12 volt headlights at their disposal, a completely climate controlled comfort pod with the most comfortable chair imaginable, metrese of high quality glass to peer through and responsible for nothing other than Paying attention to the view, and still plough over another human being. Why should the onus be on the cyclist to take every possible precaution? By that logic, the cyclist was in the wrong simply for stepping outside their house.

    5 years ago

    • avatar
      Thomas Lumley

      1. I didn’t write the statement you’re objecting to. That’s why it’s in quotation marks. The person who wrote it is at the other end of the link I provided, if you want to comment to him — you haven’t so far.

      2. We’ve already established that the victim in the Coroner’s case was wearing high-visibility clothing, so ‘blame the victim’ certainly doesn’t apply to this victim.

      3. I agree about the responsibility of drivers for a lot of serious cycling accidents. Most drivers don’t pay attention to cyclists. That’s why it’s dumb not to defend yourself

      4. It’s a good bet you spend more time in a car than I do.

      5. You ignored the rules about giving a full name if you want to post here. I let this one through as a one off.

      5 years ago