Posts by David Haywood
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Grace Dalley wrote:
I get what you're saying, but aren't there NZ figures on numbers of people cycling since helmets were compulsory? Are they included in the stats you're talking about?
Sure they are. In fact, studies of the situation in NZ have often been cited in other countries to argue against following NZ's lead on making cycle helmet laws compulsory.
Here's a summary of the latest data from the LTSA over the period 1989-2006 (unfortunately the sampling doesn't straddle the compulsory cycle helmet laws any more conveniently than that):
-- the number of cycling trips decreased by 51% from 181 to 89 million trips
-- the total distance cycled decreased by 29%, from 3.5 to 2.5 hundred-million kmAnd don't forget that the NZ population has increased significantly over this period.
Since were talking about population statistics, we can only talk about average chances of having a fatal accident, and average chances of poor health as a result of average reduction in exercise.
Of course -- sorry if I wasn't clear. I was using Jolisa's annoying helmetless cycle lady (that is, the helmetless cycle lady was annoying, not Jolisa) as a Jane Everywoman to make some generalized statements. Sorry if that was confusing.
As you so rightly pointed out earlier, this says nothing about the individual.
No actually, I was talking about a whole completely different thing (whether helmets are safe for individuals during a crash vs. the effect of the compulsory cycle helmet law on the whole population in terms of health).
I begin to realize that I am completely and utterly crap at explaining any of this. Sorry folks!
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Jolisa (one 's') wrote:
I am a fierce adherent of the helmet, and was deeply horrified to spot a woman cycling past me the other day at speed...
I'm not sure I'm making myself clear here -- the studies that I discussed on the radio say nothing about whether it's safe or not for an individual to wear a helmet -- they're talking about what has already happened in countries with compulsory cycle helmet laws.
I always wear a helmet myself. And, like you, certainly used to think that everyone should be made to do the same.
But what the studies show, is that -- if we made that woman wear a helmet -- then (on average) there's a 20 to 40 per cent chance that she would simply stop cycling.
This means two things (according to the studies):
1. If she didn't replace her cycling with another form of exercise then her increased chances of heart disease, diabetes, etc. would be much greater than the injury risk of her cycling without a helmet. Net effect: you've just shortened her life.
2. As each person stops cycling it becomes more dangerous for the remaining cyclists on the road, since they are less at the forefront of motorists minds as a potential hazard. Net effect: you've just shortened your own life.
Or to put it another way: it's not the helmets, it's how we're making them compulsory.
So it's a much more complicated issue than it seems -- and very anti-intuitive!
By the way, someone has just sent me a paper that suggests that the compulsory cycle helmet law in New Zealand costs the country $26 in health terms for each dollar it saves. I haven't checked out the paper properly yet, but -- at face value -- that doesn't sound like a sensible law to me.
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Does the statistical argument look at severity of injuries, or just number?
I think the best paper that I've looked at (de Jong, 2009) was a cost benefit analysis. It concluded that: "... only under extreme, theoretical circumstances do mandatory helmet laws not end up costing the healthcare system."
As you suggest, the two sides of the argument are about entirely different things, which could be summarized:
1. If you've just had a bicycle accident and you're flying through the air, is it better to be wearing a helmet?
2. Do compulsory helmet laws have a net beneficial effect on the overall health of society?
The answers according to the science appear (to me) to be:
1. YES (probably -- or, at any rate, I wear a helmet myself)
2. NO, QUITE THE OPPOSITE (almost certainly)
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Heather Gaye wrote:
WRT the cycle helmet thing, are there examples of countries revoking a helmet law and the number of cyclists increasing?
As far as I can ascertain, New Zealand, Australia, and Israel are the only countries with compulsory cycle helmet laws.
Israel is currently in the throes of revoking their compulsory cycle helmet law (the repeal bill passed its first reading in February). If this goes through then I guess we'll have some data to answer your question.
In Israel, as elsewhere, the debate is basically between the A&E people who claim that helmets reduce individual injuries, and the statisticians who appear to be able to prove that the law has had a detrimental effect on the overall health of society. The A&E argument is very easy to follow and intuitive; the statistical argument difficult to follow and anti-intuitive.
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Grace Dalley wrote:
Regarding force and velocity, isn't the velocity (and mass) of the cars, trucks and buses that might hit you more relevant than your own velocity as you cycle?
Yes, you're right, it is. But cycle helmets aren't designed to protect you under such circumstances.
Here's an article about cycle helmet testing by Brian Walker, whose company 'Head Protection Evaluations' is the principal UK test laboratory for helmets and head protection systems.
He notes that:
Cycle helmets are primarily designed for falls without any other vehicle involved. In many legal cases I have studied where a cyclist was in collision with a motorised vehicle, the impact energy potentials were of a level that outstripped those that we use to certify Grand Prix motor racing helmets.
The full article is here.
It's fascinating reading, although I chose to focus the radio discussion on the very solid evidence about the negative health consequences of our compulsory cycle helmet laws -- rather than the much more contentious arguments about whether cycle helmets themselves actually work.
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Hadyn Green wrote:
Is the donkey really a unicorn? I've watched it a few times and keep seeing the unicorn.
That is an excellent point! And, apart from his habit of dismantling everything in sight, this may be further indication that Bob will grow up to be an engineer (or a physicist or something else non-unicorny).
Jake Pollock wrote:
I was wondering if Bob had moved on to Woody Guthrie's children's albums, but obviously his tastes are a lot more contemporary these days.
Oh, Bob still likes old-timey music as well. But it tends to have a soporific effect on him, meaning a daytime nap, meaning he won't fall asleep at night until 1 am or some similarly ungodly hour.
I've updated the original post with a P.S.
P.S. For those of you requesting more science stuff, I'm now the science correspondent for Nine-to-Noon on Radio New Zealand. You can listen to my first piece here (it's about the science behind the cycle helmet laws and a bit of science history on Project Orion):
http://www.radionz.co.nz/audio/national/ntn/2010/06/16/science_-_david_haywood
Or as an MP3:
http://podcast.radionz.co.nz/ntn/ntn-20100616-1148-Science_-_David_Haywood-048.mp3
Feel free to discuss that here, too. FYI I've already had email from a NatRad listener saying that they hope I fall off my bike and die, so there's no need for anyone else to mention this point again (even if you feel that way)!
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RE: Chimney Sweeps/Dandelions
I was utterly entranced when I read this in Bill Bryson's otherwise very slight biography of Shakespeare. Unfortunately, as with several other "facts" cited in Bryson's books, when I thought about it for a few minutes it seemed highly improbable. Remembering my history of the Industrial Revolution, I recalled the various regulations to protect child chimney sweeps (1840s-ish), which were enacted not too long after the invention of the modern chimney brush (I think there was a patent issued about 1800, and then an improved system patented in the 1830s). So yes, it would have been quite a clever bit of poetry for Shakespeare to allude to something that wasn't invented until a couple of hundred years after his death.
Incidentally, and just to bore the socks off everyone, the chimney is a comparatively recent invention (in Britain) -- popular in dwellings only after coal became a commonly-used fuel. In Shakespeare's time (certainly his youth) chimneys would have been the province of big mansions and the like.
Jolisa wrote:
I wonder if it worked as a pun in Shakespeare's time? Or if dusting is entirely a post-17th C activity?
My OED cites the first usage of 'duster' as 1576 (when Shakespeare was 12). And certainly the Romans had a word for dust ('pulvis' from which we get pulverize; only the third time in my life that learning Latin has proven useful) -- but perhaps the Romans just left the dust lying around, as was their practice in Pompeii. I've always imagined that the Spartans would have been keen on dusting, but have no actual proof of this.
At any rate, if you want to avoid dusting, I'd suggest that you set your time machine for a whole bunch before 1564. Maybe the Pliocene?
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My Auntie Briar wrote:
David is being his usual self-effacing, modest self
First time I've ever been called that! But very pleased to have been involved with the production of the book -- even though my contribution was genuinely rather small.
Jolisa wrote:
[Quoting David Haywood:]
> Also I never noticed the pun until Jolisa
> pointed it out (above).
Actually, I had never noticed it either, even after I (apparently) pointed it out.Oh, I misunderstood you then! I had assumed the Dick Van Dyke thing must have been a pun -- how cruelly I have misjudged the fine lyricists at Disney (not to mention the genius who coached Mr Van Dyke with his remarkable Cockney accent).
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Thank you all again for the kind comments on this thread. It's been really helpful to read people's thoughts on this...
I'm heading up to Auckland for the funeral tomorrow, so it'll be very nice to commune with all my relatives up there. Emma Hart has kindly loaned me some episodes of the BBC's 'Amy Pond' television programme (I think this series may have originally aired under a different name), so this will keep me occupied during my 4-hour wait at Wellington airport.
To respond to a couple of comments at random:
I grew up learning "Golden lads and lasses must"
So did I! And remember being quite surprised when I read the official version in Cymbeline. Also I never noticed the pun until Jolisa pointed it out (above). That's how stupid I am.
You must be among the more literate of teachers of thermodynamics.
You'd be surprised! There are some very well-read engineering academics at Canterbury. And some very good writers, too. In fact, in single combat against the English Department, I think English might do much worse than they'd expect.
FYI I managed to slip in a brief mention of Wilfred Owen and Robert Graves in today's thermo lecture. I'll leave readers to figure out the connection between entropy generation in large-scale refrigeration plants and these poets.
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Many thanks for all the kind words and cyber-hugs, everyone. Yes, it's a sad time for the Haywood family -- even young Bob, who is a bit traumatized by his first encounter with the D word. We're going for a drive into the Port Hills right now as a cheer-up treat.