Did Australian helmet law “kill” UK cycling to work?

There’s a recently published article in The Conversation about common misinterpretations of research. I strongly disagree with their take on helmet legislation and I have even stronger concerns they cite the Bicycle Helmet Research Foundation as a reliable source for information. I have communicated my concerns to the article’s authors privately.

There were lots of comments about helmet legislation — both critical and supportive. Here is one from Dorothy Robinson that I found very strange.

Adding in Scotland (which used to be included in the census data but now appears to have gone its own way), UK census data on cycling to work are:
1981: 3.76%
1991: 2.97%
2001: 2.89%
2011: 2.96%

Note that no citation was given for this data and I don’t know where it exists on the web. Some UK census data for cycling to work exists here.

For many years now, Robinson and the BHRF have used census data and counts from helmet use surveys to argue helmet legislation in Australia have significantly deterred people from cycling. In the UK, cycling to work decreased 21% from before any helmet legislation (1981) to after most Australians were subjected to such laws (1991). Note that during those same years, the Australian census data reported 1.11% and 1.13% travelled to work by bicycle in capital cities.

This certainly does not mean helmet legislation in Australia had anything to do with cycling rates in the UK (this post’s title is meant to be tongue-in-cheek). Cycling in Denmark has decreased 17% since 1990 (year of the first helmet law in Victoria) and no one believes this had anything to do with Australian helmet laws. However, I think such thought experiments highlight the problems in drawing strong conclusions from such analyses.

Census data is taken over a day and successive observations are five years apart (in the UK they are apparently 10 years apart). Treating this data as a time series ignores the day to day variability in the proportions of travel modes. There are lots of factors that influence whether someone cycles (including regular cyclists). Two observations, five or ten years apart doesn’t remotely account for that.

Yearly estimates of cycling participation/amount and broad categories about cycling frequency would be an improvement. An honest assessment of the quality of the available data and its limitations is sorely needed in this area. It seems there are some that are quite content with data as long as it supports their conclusions.