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Intelligence tests are regularly adjusted so that the average person has an IQ (intelligence quotient) of 100. Since 1910, the global IQ has risen about three points per decade, a phenomenon called the “Flynn effect”, named after US intelligence researcher James R. Flynn. This means that a person who scores 100 on an IQ test today would have got a score of 130 if they had taken the test in 1910 — higher than 98 per cent of the population back then.

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