Are helmet laws suppressing cycling?
Posted: December 13, 2011 Filed under: Cycling | Tags: bicycle, Canadian Business Network, Chris Rissell, Health Promotion Journal of Australia, mandatory helmet law, Metlink, survey, Sydney, World Bank
If maps were based on time not distance, this is how big (and small) the Netherlands would look
A new Australian study has thrown more fuel on the fiery debate about whether or not bicycle helmets should continue to be mandatory. Its headline claim is 23% of Sydneysiders say they would cycle more if they weren’t obliged by law to wear a helmet.
This isn’t merely saying that some people would prefer to cycle without a helmet – it’s claiming the law actually suppresses cycling.
I lean toward the school of thought that says mandatory helmets probably do more harm socially than good, but as I’ve said before, it’s not the sort of issue that I would want to die in a ditch over. However if there were reliable evidence that compulsory helmets actually restrain cycling, that would require a rethink.
The research was undertaken by Professor Chris Rissell and his colleague, Li Ming Wen. It is published in the latest edition of the Health Promotion Journal of Australia, under the snappy title, The possible effect on frequency of cycling if mandatory bicycle helmet legislation was repealed in Sydney, Australia: a cross sectional survey.
It’s a brief and easy to read article but a summary by Professor Rissell was published on The Conversation last week, Make helmets optional to double the number of cyclists in Australia. Professor Rissell is a self-confessed cycling advocate and firmly in the activist “repeal” camp on helmets.
He and his colleague surveyed 600 Sydney residents aged 16 years and over. They found one fifth of respondents “said they would cycle more if they did not have to wear a helmet, particularly occasional cyclists”. They conclude that:
While a hypothetical situation, if only half of the 22.6% of respondents who said they would cycle more if they did not have to wear a helmet did ride more, Sydney targets for increasing cycling would be achieved by repealing mandatory bicycle helmet legislation. A significant proportion of the population would continue to wear helmets even if they were not required to do so.
Regrettably, I don’t think this study adds anything to our knowledge of whether Sydneysiders would ride more if helmets weren’t compulsory. They might, but then again they might not. The trouble is the survey relies on a hypothetical situation: “Would you cycle more often if you didn’t have to wear a helmet? Yes or No?”.
Hypothetical survey questions are notoriously unreliable. I’m not picking on the anti-mandatory helmet brigade here – I also took Metlink to task earlier this year for trying to make grandiose predictions about future public transport patronage based on a similarly unreliable methodology.
It’s standard practice to avoid hypothetical questions in surveys. Consider this advice from The World Bank publication, The Power of Survey Design:
Hypothetical questions, especially, should be avoided. People cannot reliably forecast their future behaviour in a hypothetical scenario. Thus, the questionnaire design should make careful use of this style of question.
Hypothetical questions are especially problematic when respondents are asked to predict an activity they’ve had little experience of. The Canada Business Network advises questionnaire designers, if possible, to “avoid hypothetical or future intentions questions:
Hypothetical questions force the respondent to provide an answer to something he or she may never have thought about and, therefore, the respondent may not be able to provide an accurate response.
The authors should’ve been alerted that all might not be right when they found 40% of those who say they’d cycle more if helmets weren’t compulsory, also say they support mandatory helmet legislation. Yes, there’re scenarios where it’s conceivable someone could hold both views simultaneously, but 40%?!
The authors implicitly concede hypothetical questions are of little value when they say “the relationship between intent to perform a behaviour and actual behaviour (for example, helmet wearing) is not known”. And they effectively throw in the towel when they say “if only a half or even a quarter of these people who say they would ride more actually did so, our data suggest that the Sydney cycling participation targets would be easily reached”. A “quarter” is just 6% of the sample! In fact there’s no rhyme or reason for choosing “if only half or even a quarter” in preference to, say, “if only a tenth or even 1%”.
The survey was part of an omnibus telephone survey covering a range of topics, so the researchers only got to ask four questions specifically about cycling. This limited their ability to investigate what respondents really meant by their answers to the hypothetical question. There are also some technical issues with the study like leading questions and no data on the response rate.
So, closer inspection shows there’s nothing in this study that persuades me mandatory helmets are a key obstacle to wider cycling in this country. They’re not helpful, but they’re not the main problem either. There are some other interesting aspects reported by the study which I hope to come back to another time.
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