How Not To Assess Risk: Falling in Holes vs. Drowning · Wednesday June 27, 2007

Jesse Walker over at Reason Magazine’s excellent Hit and Run blog points to a Guardian article on an essay in the New England Journal of Medicine (subscription required) that reveals the massively insignificant fact that since 1990 more people in the US have died from falling in holes dug in the sand (16) than from shark attack (12). This alone isn’t really noteworthy, except possible for bar bet use, but the final paragraph of the Guardian article is:

Although such incidents were extremely rare, Dennis Arnold, who runs a beach patrol at Martha’s Vineyard, off Cape Cod in Massachusetts, said lifeguards were under orders to stop children digging deep holes. Occasionally some parents protest, he said. “They’ll say ‘You’re ruining my kid’s day!’ and I say ‘I don’t care!’,” Mr Arnold was quoted as saying.

This is a clear illustration of one of the problems of perceived vs. actual risk enumerated by Bruce Schneier in Beyond Fear:

People exaggerate spectacular but rare risks and downplay common risks. They worry more about earthquakes than they do about slipping on the bathroom floor, even though the latter kills far more people than the former. Similarly, terrorism causes far more anxiety than common street crime, even though the latter claims many more lives. Many people believe that their children are at risk of being given poisoned candy by strangers at Halloween, even though there has been no documented case of this ever happening.

The United States Lifesaving Association reports 461 drowning deaths on US beaches in the 2002-2005 period alone. That’s over 28 times as many deaths in less than one third the time.

So what do you suppose the end result of turning lifeguards into The Hole Digging Police increasing the lifeguards’ attention to hole digging will be?

Hint: it won’t add to the amount of time they spend watching the water where, you know, people drown.

Let’s hope Mr. Arnold is in charge of a very small, very unpopular beach that these aren’t new orders.

edit (7/8/07): As I clarified in this comment on Bruce Schneier’s post on this subject, my opposition is to any increased attention to hole digging based on this study. It is not clear from the Guardian article whether Mr. Arnold is referring to new or existing orders, hence the modifications above.

— Rod Knowlton

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Tell me what you know (comment)

This kind of thing sometimes really infuriates me. I can remember making a trip to Toronto during the SARS outbreak, and trying to convince people that the risk of contracting SARS was orders of magnitude less than the risk of tripping in front of a Taxi. 257 cases, 33 fatalities (source) in a city of 4.7M people ... phew.

But I wanted to share an interesting observation made to me by a transport systems analyst a couple of weeks ago that is at least partly analogous to your lifeguard.

Spending money on rail safety can actually increase the mean number of fatalities per journey mile.

It seems ridiculous, but in a country with private train operating companies, the cost of the rail safety improvements are likely to be passed on to the consumer in the form of increasing ticket costs. Increasing ticket costs will clearly push people to use other forms of transport, nearly all of which are inherently less safe than the railways.

As you point out, there is a twisted irony in the fact that the rarer the type of accident, the more likely it is to receive press coverage. Every major rail crash in the UK has had an associated enquiry, despite the fact that 9 people a day die on the roads with a fatality rate of around 5.31 per billion passenger km, as compared with the 10-50 deaths per year on the railways, with a fatality rate of all of 0.4 per billion passenger km.

Oh, if only policy makers could work on the basis of evidence rather than public opinion: how much more progress would we make!

— Nick Stenning · Jul 5, 11:30 AM · #

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