Hard News by Russell Brown

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Hard News: Fear of Cycling

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  • Carol Stewart, in reply to Bart Janssen,

    So I searched the Cochrane reviews for a complete unbiased meta-analysis, and found two that seem relevant.
    One concludes:
    "Helmets reduce bicycle-related head and facial injuries for bicyclists of all ages involved in all types of crashes, including those involving motor vehicles. Our response to comments from critics are presented in the Feedback section."

    And the other concludes:
    "Bicycle helmet legislation appears to be effective in increasing helmet use and decreasing head injury rates in the populations for which it is implemented. However, there are very few high quality evaluative studies that measure these outcomes, and none that reported data on possible declines in bicycle use."

    Wellington • Since Jul 2008 • 822 posts Report Reply

  • Jon Briggs, in reply to Russell Brown,

    I had to look up what Bete Noir meant, but I am glad that I did - always more comfortable being able to hold onto your prejudices ;)

    Since Dec 2008 • 27 posts Report Reply

  • Russell Brown, in reply to Carol Stewart,

    So I searched the Cochrane reviews for a complete unbiased meta-analysis, and found two that seem relevant.

    Thanks for doing that. It does seem odd that no one else had hit the Cochrane button :-)

    Auckland • Since Nov 2006 • 22756 posts Report Reply

  • Bart Janssen, in reply to Carol Stewart,

    So I searched the Cochrane reviews for a complete unbiased meta-analysis, and found two that seem relevant.

    Which is fine except that their only assessment is from 2008.

    I'm not sure why you are unwilling to accept recent risk analysis work as evidence. The maths is straightforward, unless you make extraordinary assumptions then then cycle helmet laws have a negative public health outcome.

    It essentially means this discussion can go no further. Which is fine, I think every opinion and reckon has been shared by now and there are plenty of links to data in this thread now for people to read.

    It does seem odd that no one else had hit the Cochrane button :-)

    It's not a very useful source outside medical research and definitely not useful for someone used to reading scientific literature directly (providing you have access to that literature) - also my opinion of it is coloured by knowing some of the people who've ended up working there. It does a good job in fields where publications are often ... er ... less well peer-reviewed and it is targeted at a lay audience which is helpful.

    Auckland • Since Nov 2006 • 4451 posts Report Reply

  • Carol Stewart, in reply to Bart Janssen,

    Cochrane reviews are useful for assessing public health interventions which is what is under discussion here. Yes sure they are a little out of date. I'm quite willing to familiarise myself with recent risk analysis work.

    Wellington • Since Jul 2008 • 822 posts Report Reply

  • linger,

    Neither Cochrane metaanalysis cited really adds anything.

    The first is not really relevant to the wider population risk analysis. It concludes that helmets improve outcomes from an accident, once that accident occurs: but that has never been subject to question.

    The wider questions of whether helmet laws end up increasing the accident rate per cyclist , and whether cycling leads to improved health, are simply not addressed.

    The relevant conclusion of the second study is simply that (in 2008) there hadn't been much study into whether helmet laws affected cycling rates. That is not a statement negating the possibility of any such relationship.

    Expanding on my earlier "path-dependence" comment: there are a number of features of the way the NZ helmet law was introduced that amplified its chilling effect on cycling uptake, and it is for these reasons that I think repealing the law would be insufficient by itself to recover the popularity of cycling to pre-law levels.
    (i) an effective, prolonged, emotive campaign -- delivered via a medium which was at the time focussed on a very small number of state-owned outlets -- first arguing for the law change, and then informing the public of the new law, emphasising the dangers of helmetless cycling. It was a campaign built on fear. Such campaigns are easy to conduct, but just about impossible to reverse by the same mechanism, especially since there is no longer a single platform on which the audience is as concentrated.

    (ii) a fine level imposed equivalent to the cost of a bicycle (though in practice, if I remember correctly, there was a grace period during which helmetless cyclists were warned rather than fined). Such a cost is prohibitive for many cyclists, and particularly for children. An interim measure worth looking at to evaluate the effect of this feature alone would be to keep the law in place, but to remove the fine, with offenders only to be warned.

    Whatever happens to the helmet law, other measures would also have to be pursued to increase the safety of the cycling environment (increasing participation, improving infrastructure, and educating motorists).

    Tokyo • Since Apr 2007 • 1890 posts Report Reply

  • Carol Stewart, in reply to linger,

    OK, having done more reading, including this 2015 meta-analysis by some public health folks in Ontario, I understand the arguments being advanced here. One question I have is whether the observed reduction in cycling participation following the NZ helmet law can be completely attributed to the law (taking account of those implementation features you mention), or whether there were other concurrent societal factors that may have played a role.

    Wellington • Since Jul 2008 • 822 posts Report Reply

  • Kevin McCready,

    I'll get to the de Jong study ASAP. Meanwhile, be wary of Cochrane =
    https://kmccready.wordpress.com/2009/04/03/cochrane-collaboration-failure/

    Auckland • Since Jun 2013 • 119 posts Report Reply

  • Kevin McCready,

    Oh, and for access to academic papers you can't go past the free Scihub =
    http://sci-hub.cc/

    Auckland • Since Jun 2013 • 119 posts Report Reply

  • Carol Stewart, in reply to Kevin McCready,

    Meanwhile, be wary of Cochrane

    Well, OK, but have you got a better alternative?

    Wellington • Since Jul 2008 • 822 posts Report Reply

  • Moz, in reply to Carol Stewart,

    whether there were other concurrent societal factors that may have played a role.

    That's hard, because the laws were a result of a very public campaign to emphasise the gory dangers of cycling. Untangling the two might be best done by removing the law and just carrying on regardless, but you're likely to get a similar media campaign encouraging people to cycle if you do change the law (or at least a renewed media focus on those campaigns).

    One thing you can look at if you're interested is bike hire schemes. The "public bikes" all over the world have been very successful... except where mandatory helmet laws apply. But again, much of the attention paid to this subject comes from people campaigning against bike helmets so it's often hard to untangle.

    Sydney, West Island • Since Nov 2006 • 1198 posts Report Reply

  • Kevin McCready,

    Ok, so I've checked the de Jong abstract. It proposes a model (hmm that could end badly) that says helmet laws reduce cycling numbers and therefore people, on a population level, don't get exercise and die earlier. Correct me if I'm wrong but this is childish and should not have been published. Wouldn't it fail a First Year stats assignment? Where's the evidence that a shortfall in cycling wasn't taken up by more walking, more swimming, more gym, more whatever?

    Auckland • Since Jun 2013 • 119 posts Report Reply

  • Moz,

    It is important to note that both sides can be right. Making helmets mandatory does reduce population head injury rates. Making helmets mandatory also raises death rates and reduces QALYs, but with a significant lag. It's win-win :)

    We can argue about the mechanism (protecting heads vs discouraging cycling - but note that helmet law advocates accept reduced cycling as a fair price for the reduction in head injuries), and likewise the lag makes small changes very easy to argue about (sadly for academics individuals don't stop cycling and immediately become obese and sedentary, and sadly for everyone starting to exercise doesn't immediately make someone trim and fit).

    Sydney, West Island • Since Nov 2006 • 1198 posts Report Reply

  • Kevin McCready,

    BTW I don't regard the cyclinghelmet.org site as a reliable source. It seems that every time a cycle hire business goes bust AND that business is in a jurisdiction that has mandatory helmet laws the website says "See I told you, it proves helmet laws are bad." FFS.
    eg =
    http://www.cyclehelmets.org/1207.html?NKey=5

    Auckland • Since Jun 2013 • 119 posts Report Reply

  • Moz, in reply to Kevin McCready,

    I already said that. And I think it's perfectly reasonable to follow up a long article describing the problems with bike hire schemes and helmets with a short note that "the expected outcome has occurred again".

    But when they are the only people covering the topic, what else can we do? Should I not mention evidence that doesn't meet your extremely high standards?

    Looking at Chris Rissel is instructive - he was vigorously criticised for modelling errors but also for not accounting for corrections to data he relied on that were made after he published. When he fixed that he couldn't get the paper published.

    But then other research has found that most "peer reviewed" papers have major errors and then we get into the more general reproducability crisis. It may well be that if a determined critic looks at *any* paper they will be able to make it look suspect. I'm not saying that science is pointless, just that if you don't want to accept a given conclusion you can always find a reason.

    Sydney, West Island • Since Nov 2006 • 1198 posts Report Reply

  • Kevin McCready,

    Moz I think you misunderstand how science works. It's a series of probability statements. You don't REALLY get to pick and choose. You can pick and choose only according to the probability values you prefer. So you get to say "The probability that gravity will plummet me to the bottom of the cliff if I step off is 99.9999999999%, but I'm going to step off anyway because it's still not a certainty and my extremely high standards of 100% haven't been met yeeeeeetttt - splatttt!!!" The probability that the de Jong model represents reality is about zero according to my back of the envelope calculation. So, ummm, I think I'll keep wearing my cycling helmet.

    Auckland • Since Jun 2013 • 119 posts Report Reply

  • linger,

    Once again, it's not about whether you wear your helmet or not (though you should). The argument is not (and the model does not imply) that one cyclist choosing to wear a helmet somehow magically increases the danger to other cyclists.

    Tokyo • Since Apr 2007 • 1890 posts Report Reply

  • Bart Janssen, in reply to Kevin McCready,

    Correct me if I'm wrong

    You are wrong. Utterly wrong. So wrong you should slap yourself in embarrassment.

    You cannot just read an abstract of such a paper and expect to understand what is being said.

    The authors build a comprehensive model including all the variables discussed here (and more) and then run the model for a range of assumptions for those variables including estimates of those variables based on data from a bunch of countries.

    If you'd actually read the paper you'd know the authors discuss and account for substitution of exercise so your little rant about the paper shouldn't have been published because you thought of something - is just silly especially because you couldn't be bothered reading the paper.

    The short conclusion is
    Unless you assume helmets completely eliminate head injuries
    AND
    the law causes a 100% uptake of helmets (from 0 to 100%)
    AND
    there is no effect on cycling numbers from the law

    then in all cases the model shows a negative health outcome from the helmet law

    For all reasonable assessments of the variables in the model (based on data from a range of countries) a helmet law is a massive negative health outcome.

    Frankly at this point Kevin you sound like a climate change denier "ooo a mathematical model that can't be any good" as if maths and risk analysis wasn't a real science.

    If you can't be bothered reading the literature before you criticise it, you really are just a troll.

    Sorry folks this kind of stuff pisses me off and I'm already tired and grumpy so sorry if this come across too strong for the one or two still reading - but I spend way too much time defending science against drivel like Kevin's to have much patience any more. FFS "I didn't read the paper but the authors are still wrong" grrrr.

    Auckland • Since Nov 2006 • 4451 posts Report Reply

  • Bart Janssen, in reply to Kevin McCready,

    The probability that the de Jong model represents reality is about zero according to my back of the envelope calculation.

    How the hell would you know - you didn't read the paper

    Auckland • Since Nov 2006 • 4451 posts Report Reply

  • linger,

    Oh -- and one reason why NZ's experience is used as the reference point for assessing the effects of helmet laws is that we introduced our helmet law ... and, rather stupidly, did nothing else to increase the safety of cyclists. Basically, in one of the earliest implementations of the "user-pays" philosophy, we chose the one solution that put all compliance costs on individual cyclists, and ignored anything that would involve increased public expenditure.

    Tokyo • Since Apr 2007 • 1890 posts Report Reply

  • Carol Stewart, in reply to linger,

    That's a good point.

    Wellington • Since Jul 2008 • 822 posts Report Reply

  • BenWilson, in reply to Bart Janssen,

    the authors discuss and account for substitution of exercise

    They do, and it's a very cunning accounting indeed. The substitution can be accounted for by varying v, the health benefit of every kilometer of accident free cycling. I was interested in how they attained a reasonable figure for it, but the answer is that if you look at equations (3) and (4) they eliminate v completely from the equation for phi, which is value they are interested in calculating, the (net health impact of helmet law)/(Helmet preventable health cost).

    So they don't have to estimate it at all. It occurs as a part of a number of variables that they can estimate from actuarial data, and in the manipulation cancels itself out. You probably could also work out v, but they were not interested in it, and it does not need to be estimated for phi to be estimated.

    Wouldn’t it fail a First Year stats assignment? Where’s the evidence that a shortfall in cycling wasn’t taken up by more walking, more swimming, more gym, more whatever?

    No. This is well beyond first year statistics (I'm 4th year myself right now so I can say this with confidence). It's a detailed and statistically sophisticated study undertaken by a very competent actuary with the express purpose of informing public policy, giving the entire detail of the formula and estimation values. In some cases the phi values come out positive, with some choices of parameters. It looks like Italy is that dangerous to cyclists that the helmet laws probably are a good idea, if your belief about the parameter beta (the benefit-cost ratio of unhelmeted cycling) is especially low.

    Auckland • Since Nov 2006 • 10641 posts Report Reply

  • Kevin McCready,

    Bart I'm happy to be wrong, if I'm wrong. Please email me the paper.
    =
    kevin 1 mccready at gmail dot com

    Auckland • Since Jun 2013 • 119 posts Report Reply

  • David Hood,

    Does the decrease in the number of cyclists also decrease the incidence of pedestrian vs cyclist injuries - These wouldn't get tracked if you were basing measures of injury on NZTA figures via police reports, as I understand it the NZTA figures are essentially "car vs. ..." (for example if you look at hospitalisations I understand the leading injury for cyclists is themselves- falling over when no other party is involved).

    Dunedin • Since May 2007 • 1445 posts Report Reply

  • linger, in reply to David Hood,

    In the NZ case, historically, the answer would have to be “not much”, because cyclists and pedestrians weren’t supposed to be sharing paths. Shared-use paths are a more recent development, and are still not widespread enough to affect national-level statistics.

    Also, if there were any appreciable decrease in cyclist-pedestrian injuries, it would have to be offset against the increase in pedestrian-vs.-car collisions resulting from the increased traffic density resulting from the decrease in cyclists. And the latter would naturally be expected to have the larger impact.

    So my guess (and it has to be a guess, because, as you suggest, the reporting rate for pedestrian-vs.-cycle incidents is unreliable at best, partly because the consequences are more likely to be negligible) is that including effects on pedestrians would not alter the overall case for increasing cycling uptake, and may even strengthen it.

    Shared cycle/pedestrian pathways may increase cyclist-pedestrian collisions, but overall are a positive development because they help isolate cyclists – and pedestrians – from motorists (where collisions can have much more serious consequences). Though it would be better to have dedicated cycle-paths and dedicated walkways.

    Tokyo • Since Apr 2007 • 1890 posts Report Reply

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