Tuesday, January 19, 2010

Helmet law rebound effects and the success of terrorism

I write regularly about rebound effects - those unintended consequences that occur due to behavioural adjustments.   I wrote my Master’s thesis on the rebound effects from energy efficient technologies and household energy conservation behaviour (a good summary is here, my thesis is here, a draft paper on household conservation is here, and a draft paper on the effect of government environmental subsidies is here)

I have written about rebound effects from using photovoltaic panels.  The rebound effect from recycling, which enables us to use even more of the raw material we are trying to conserve. Recently, I wrote about the potential rebound effect from sunscreens – because we don’t have the immediate signal of sunburn to tell us that we have had enough sun exposure, we tend to spend more time in the sun.

One area I am particularly adamant that unexplored rebound effects exist is in preventative health care costs – by preventing one disease, we enable people to succumb to other diseases, which have potentially greater treatment costs.

But these sly rebound effects do not end there.

Today I read, in a book on probability and randomness no less, that after the September 11 terrorist attacks the amount of long distance commuting by car increased dramatically due to both fear and forced cancellation of flights.  Because of all this extra driving, there were an estimated 1000 extra road deaths than had people continued to fly as their means of transport.  The forgotten death toll?  A win for terrorists? Or simply unintended consequence caused by human adaptation to circumstance.

Recently a paper was published (see comments and link here) to support the fact that bicycle helmet laws, while reducing cycling fatalities, also reduce the rate of cycling.  While the paper does not go into detail on what people are instead doing, we can use this main point to hypothesise a little about what other unintended consequences might arise.

First, the main finding is that helmet laws reduce youth cycling, and subsequent cycling in adult life.  For youths, we might suggest that instead of cycling they may be skateboarding or rollerblading instead, without helmets.  They may participate in idle activities such as video games, potentially contributing to diseases associated with lack of exercise.  There are infinite possibilities about what youth are doing instead, and not all are safer in the short or long run.

This article suggests that when the decline in cycling is factored in, helmet laws result in a net cost to the community.  Take special note of the comments.  More people suffer severe head injuries from walking, yet there are not helmet laws for that. 

Finally, if you are still interested in helmet rebound effects I suggest you have a quick read here

At the end of the day, if we don’t consider these rebound effects in our policy decisions, nor do we assess the effectiveness of policy in retrospect (why not have a 10 year review or some such thing), then we will continue to make poor decisions for the community as a whole. 


More about helmet laws at the Freakonomics blog


  1. This was on the Howies website today, how apt! http://brainfood.howies.co.uk/wp-content/uploads/2010/01/striphandler.ashx_.gif

  2. This rebound effect makes my head spin...

  3. Rebound effect
    Tasmania - first state to introduce flouride into water supplies.
    In 2010 Tasmania has the worst dental health and cavity rate of any australian state.

    In Europe countries without flouride in the water have better dental health than australia.