Lies, damn lies and incident statistics

We’re all terribly bad at interpreting statistics. It’s the way are brains are wired. We tend to leap to the wrong conclusions. And we’re heavily influenced by context and spin. Politicians, marketing managers and journalists have known and exploited this for many years. It’s a trick that all security managers need to master in order to get their points across. Appealing to the rational side of users and customers is generally doomed to failure.

I always try to get to the bottom of statistics. So I was naturally intrigued when I read the headline “Zebra crossing road deaths treble” in today’s Daily Telegraph. It smacked of spin. Reading further I noted that annual deaths had risen from three a year to nine. Now, that’s a very small increase in numbers. I wondered if it might have perhaps been no more than a random fluctuation.

Like most people, I find it impossible to judge these things intuitively, so I made a few rough calculations. These indicated that if the average was three a year, then there’s only a one in five chance of exactly three occurring. But the chances of nine occurring are much smaller, almost an order of magnitude less. So it seems there might be something significant behind this change.

But once you start digging it gets really complex. There are so many factors. The Telegraph points out lots of potential causes, but most of them are not things that have changed in the last year. The real cause is less relevant, however, as long as it provides a vehicle for airing complaints about the design of crossings, the level of fines for motorists who ignore them, and how the UK pedestrian safety record compares with other countries.

This type of spin is a phenomenon we simply have to get used to. We’re entering an age when faster judgements have to be made on growing amounts of information. And the data is getting increasingly easy to change, annotate and present out of context. The facts matter less than the perception. That’s why politicians are less concerned with actually fixing the problems than with convincing us they’re competent to do it. But as Douglas Adams cautioned, once you’ve proved that black is white, you’ll probably go on to get yourself killed on a zebra crossing.

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