What is IQ?
A famous number, often misunderstood. A short history and a user's guide.
The intelligence quotient (IQ) is a score from standardized tests that places a person's reasoning performance relative to people of the same age. It doesn't measure “intelligence” as a whole, but a set of abilities: logical reasoning, verbal comprehension, working memory and processing speed.
Where does IQ come from?
1905: Binet and Simon
At the request of the French school system, Alfred Binet and Théodore Simon built a scale to identify children who needed extra support at school. It estimated a “mental age” from exercises of increasing difficulty.
1912: the “quotient”
German psychologist William Stern proposed dividing mental age by actual age. Lewis Terman multiplied that ratio by 100 in his American version of the test (the Stanford-Binet, 1916): IQ was born.
1939: Wechsler and modern IQ
David Wechsler dropped the idea of mental age, which didn't work for adults. He compared each person to their age group on a normal curve with a mean of 100 and a standard deviation of 15. Today's tests still follow that principle (WAIS for adults, WISC for children).
How is it measured today?
A full assessment takes one to two hours with a psychologist and combines several subtests. Among them, matrices hold a special place: popularized by John Raven in the late 1930s, they are grids of patterns where you find the missing piece. Free of words and general knowledge, they measure what's called “fluid” reasoning. They're the main type of puzzle in our test.
To learn how to read a score, see the IQ scale and percentiles.
What IQ predicts (a little)
On average, IQ scores correlate with academic success and some aspects of career success. But a statistical correlation says almost nothing about an individual: motivation, environment, health and luck weigh heavily.
What it doesn't tell you
- Creativity, emotional intelligence or practical talents.
- A fixed state: scores vary with fatigue, stress or practice on the exercises.
- Your worth. An online IQ test, ours included, is a logic game that gives an estimate, not a diagnosis.