Sample minds

June 2, 2009

Tom Whipple
253 words
5 December 2008
The Times
Times2 5
English
(c) 2008 Times Newspapers Limited. All rights reserved

“Common sense,” Einstein said, “is the collection of prejudices acquired by the age of 18.” The Enlightenment was the victory of science over common sense. Common sense tells us that the Earth is flat and is circled by the Sun. The slow accumulation of data, powering the steamroller of science, tells us that both assumptions are false.

Maybe common sense needs rehabilitating. Earlier this month, the Daily Mail told us that “teenage boys believe using pressure and alcohol to get girls into bed is ‘acceptable'”.

The data came from a study of 35 14, 15 and 16-year-olds of both sexes who were asked, in small gender-segregated groups, to talk about attitudes to sexual relationships. They were selected from those visiting sexual health clinics, in areas with high teen pregnancy rates.

Imagine you are in a room, asking teenage boys about sex. Since they have all visited sexual health clinics in areas where teen sex is a problem, would you draw conclusions from them about the non-sexually active population? Would their answers be a story?

Last year the United Nations admitted that it had overestimated Aids prevalence in Africa. The reason? Sampling is difficult in Africa, so they took the only figures they had: HIV prevalence among women in antenatal clinics. So their sample population consisted entirely of women who had had unprotected sex.

Numbers are imperfect, because research is imperfect. Sometimes interpretation requires a little common sense.

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