IQ: How important is a high IQ?

A speech by London Mayor Boris Johnson has raised the issue of IQ and how it relates to success. So just how important is it, asks Denise Winterman.

Boris Johnson's comments about IQ in a speech at the Centre for Policy Studies on Thursday have attracted criticism but they have also raised a big question - does IQ matter when it comes to wealth and being successful in business?

Huge amounts of research have been done on IQ - intelligence quotient - and many claims made about it. Holidays and junk food can make IQ drop while being breastfeed and a big head can make it go up. These are just a few assertions discussed in an article in Psychology Today.

IQ tests as we know them today were developed in the early 1900s, the first being the Stanford-Binet intelligence scales. Many have since been developed and measure slightly different things, say psychologists. The Stanford-Binet and the Wechsler intelligence scales remain the most popular.

The average IQ score in the UK is 100, according to British Mensa. But even if you score at the lower end of the scale all is not lost as IQ can change, say experts.

"Given different environments and opportunities IQ can develop and grow," says Professor Joan Freeman, a developmental psychologist who runs the country's only dedicated practice for gifted children. "Something as simple as a bad cold can make IQ go down temporarily."

Also, IQ is not the be-all and end-all when it comes to being a high earner. A study by Ohio State University's Center for Human Resource Research is among several that suggest IQ has no relationship to wealth. This is because the tests only measure a person's cognitive ability and being successful is about much more, says Freeman.

"IQ tests don't measure other qualities such as personality, talent, persistence and application. You might not have a high IQ but if you have a gung-ho personality then you may use what you have more effectively than someone with a high IQ... I regard IQ like a muscle, you may be born with the muscles of an Olympiad but if you don't use them they will diminish."

Which leads to the next big question - is going to the mental gym as hard as going to a physical one? Let's hope not.

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