The idea that intelligence can be measured by IQ tests alone is a fallacy according to the largest single study into human cognition which found that it comprises of at least three distinct mental traits.

IQ tests have been used for decades to assess intelligence but they are fundamentally flawed because they do not take into account the complex nature of the human intellect and its different components, the study found.

The results question the validity of controversial studies of intelligence based on IQ tests which have drawn links between intellectual ability race, gender and social class and led to highly contentious claims that some groups of people are inherently less intelligent that other groups.

Instead of a general measure of intelligence epitomised by the intelligence quotient (IQ), intellectual ability consists of short-term memory, reasoning and verbal agility. Although these interact with one another they are handled by three distinct nerve “circuits” in the brain, the scientists found.

“The results disprove once and for all the idea that a single measure of intelligence, such as IQ, is enough to capture all of the differences in cognitive ability that we see between people,” said Roger Highfield, director of external affairs at the Science Museum in London.

“Instead, several different circuits contribute to intelligence, each with its own unique capacity. A person may well be good in one of these areas, but they are just as likely to be bad in the other two,” said Dr Highfield, a co-author of the study published in the journal Neuron.

The research involved an on-line survey of more than 100,000 people from around the world who were asked to complete 12 mental tests for measuring different aspects of cognitive ability, such as memory, reasoning, attention and planning.

The researchers took a representative sample of 46,000 people and analysed how they performed. They found there were three distinct components to cognitive ability: short-term memory, reasoning and a verbal component.

Professor Adrian Owen of the University of Western Ontario in Canada said that the uptake for the tests was astonishing. The scientists expected a few hundred volunteers to spend the half hour it took to complete the on-line tests, but in the end they got thousands from every corner of the world, Professor Owen said.

The scientists found that no single component, or IQ, could explain all the variations revealed by the tests. The researcher then analysed the brain circuitry of 16 participants with a hospital MRI scanner and found that the three separate components corresponded to three distinct patterns of neural activity in the brain.

“It has always seemed to be odd that we like to call the human brain the most complex known object in the Universe, yet many of us are still prepared to accept that we can measure brain function by doing a few so-called IQ tests,” Dr Highfield said.

“For a century or more many people have thought that we can distinguish between people, or indeed populations, based on the idea of general intelligence which is often talked about in terms of a single number: IQ. We have shown here that’s just wrong,” he said.

Studies over the past 50 years based on IQ tests have suggested that there could be inherent differences in intelligence between racial groups, social classes and between men and women, but these conclusions are undermined by the latest findings, Dr Highfield said.

“We already know that, from a scientific point of view, the notion of race is meaningless. Genetic differences do not map on to traditional measurements of skin colour, hair type, body proportions and skull measurements. Now we have shown that IQ is meaningless too,” Dr Highfield said.

The smarter test: Try it yourself

These questions evaluate the three components of intelligence.

Memory

Candidates would be asked to remember and repeat a sequence, digits 3, 6, 1, 9, 6, 2, 5, 3 for example

Reasoning

If Box A is twice as big as Box B and Box C is half the size of Box A, which is bigger, C or B?

Verbal skills

If you are given the statement, “A does not follow B”, and then shown the letter B followed by the letter A, is the statement true or false?