Risk homeostasis

Reading the occasional off-hand remark about helmets in Chris's blog has led me to take a look at risk homeostasis. It is one of the arguments advanced by the "anti-helmet" web sites that Chris has provided links to. The basic idea is that people tend to maintain a constant level of absolute risk in the face of wide variations in the safety of a particular activity. For instance, if we improve roads — better surfacing, cambered bends, etc. — people will tend to drive faster, so that their chance of adverse consequence per unit time stays the same (although the chance of a crash per unit distance would go down). I personally find this rather disturbing, and wish it were not true. Unfortunately, there is plenty of evidence that it is the case. The classic studies were done on road safety, but the idea is now being applied to other areas too. For instance, some poeple have the perception that antiretroviral drugs make HIV much less of a problem in the "developed world" these days, and sure enough, infection rates here seem to be rising.

Since I find it rather depressing to think about this in the context of people's lives at risk, I started to wonder whether it applies to software development. If we insist that people build the full train before they put back their changes, will they put back stuff that is known to compile, but is less likely to work (correctly)? If we insist that people write unit tests for their code, will they then spend less time thinking about whether their algorithm really works?

I don't have any answers for these questions, but I'm going to be on the lookout for examples.

Comments:

I don't know about software but I think your observation here regarding risk homeostasis must also be valid when it comes to taking insurance, which is very much like paying and wearing a helmet. I think the insurance companies, which have the greatest amount of data, have proven, by the institution of incentives and punishments for safe and risky behaviors, that homeostasis in risk is indeed the case. Otherwise, why would one need further incentives and punishments other than the insurance one takes. (The insurance, then, becomes just a recurring source of revenue for someone who is not about to take any risks on the one against whose risks he insures.)

Posted by M. Mortazavi on June 05, 2005 at 05:01 PM PDT #

The big difference between insurance and cycle helmets is that insurance does have proven benefit when it is needed. Unfortuantely cycle helmets have no such proven benefit. They are simply not designed to cope with the kind of accidents that people wear them to protect themselves.

This makes it even more frightening that riders will take more risks when wearing them. Most frightening is the thought that drivers will sub conciously take more risks with a helmeted rider.

Oh and nice banner on the blog Terry!

Posted by Chris Gerhard on June 05, 2005 at 07:48 PM PDT #

In his book Hidden Order: The Economics of Everyday Life, David D. Friedman says to imagine the effect of drivers' behavior if the airbag on the steering column were replaced with a big spike.

Posted by Tom Harrison on June 06, 2005 at 12:18 AM PDT #

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