Lies, damned lies, and a coin toss

June 2, 2009

Tom Whipple
374 words
10 April 2009
The Times
1
7
English
(c) 2009 Times Newspapers Limited. All rights reserved

his week, Bad Statistics would modestly like to suggest a new clause in the press code of conduct. If a paper reports on an annual statistic one year, it should do so the next. We will outline our case with the statistician’s oldest metaphor: the coin toss.

When you toss a coin, there are three possible outcomes: heads, tails or standing on its edge. The same is true with annual statistics. The 2009 UK widget output can be higher than 2008, lower or exactly the same. Given the scale of our widget-making industry, the chances of it being exactly the same is like a coin landing on its edge.

So even if a statistic — teen pregnancies, say — stays at the same level, it will probably have either decreased slightly (not a news story) or increased (preferred terms are “soared” or “spiralled”). After ten years of small but steady decline, this year teenage pregnancies in England and Wales “spiralled” (© the Daily Mail) from 40.9 per 1,000 15 to 17-year-old girls, to 41.9.

This was an especially useful statistic, as it coincided with news that a 13-year-old boy had fathered a child. Will teenage pregnancy rates be reported next year? Well, that is entirely dependent on whether they rise.

Even if they don’t, something else — truancy rates perhaps, or glue-sniffing — is bound to oblige. A more sophisticated variation of this technique has proved effective in crime statistics.

Has crime inconveniently fallen this year? No matter, lots of different crimes are measured, each equivalent to a coin toss; one of them is bound to have come up heads. So in 2007, when crime fell, we wrung our hands about an increase in “alcohol-related violence between 3am and 6am”. In 2008, when crime also fell, pre-dawn attacks had inexplicably dropped from the news agenda to be replaced with concerns about school-age burglars.

This is genius. If every social phenomenon in the UK remained constant every year for ever more, the press would still be able to report that Britain is going to hell in a handcart 50 per cent of the time..

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