A percentage point

June 2, 2009

Tom Whipple
360 words
12 September 2008
The Times
Times2 5
English
(c) 2008 Times Newspapers Limited. All rights reserved

Shampoo adverts follow a comfortingly reliable formula. First, swishy models with swishy hair swish across the screen. Then “The Science Part” shows computer-generated nano-particles livening up dead roots and informs us that “68.18 per cent of Superhair hair product users had swishier hair”. In tiny print across the bottom are the words “15 out of 22 respondents noticed positive results”.

The great thing about percentages is that they make samples seem bigger, results more accurate. It all seems more – well – sciencey.

And these techniques don’t just apply to hair. We learnt in the Daily Mail this week that, since the introduction of a curfew for teenagers in Redruth, crime has “plunged” by 15 per cent. Excellent news. And how many crimes was that? Fifteen. In fact, the paper got its sums wrong: it said that crime had dropped from 121 incidents in August last year to 106 this year, a fall – using its own data – of 12 per cent.

Reporting on a study by the Equality and Human Rights Commission into the “concrete ceiling” faced by women, various newspapers told us this week that the proportion of women in the Cabinet has fallen from 34.8 per cent in 2006 to 26.1 per cent. How many is that? From eight to six. There is definitely cause for concern about equality in many professions – but would papers really have reported a drop of two people as significant if expressed in that way? Put it in percentages, though, especially with decimal points, and suddenly it has gravitas.

Percentages are great for simplifying changes in large numbers, or numbers that themselves involve decimal points, such as prices. But when the numbers involved are both small and whole, it is difficult to see why we need to convert them to percentages. All that it achieves is to move the consumer of the statistics further from the raw data itself so that they are less able to evaluate its importance. Unless, of course, that is the point.

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