What is IQ?
IQ, short for intelligence quotient, is a score that compares how well you reason with how others of your age do.
A score relative to other people
An IQ score is not a count of right answers. It shows where your result falls compared with a large group of people of the same age. Modern tests set the average at 100 and the standard deviation at 15, so about two thirds of people score between 85 and 115.
Where the name comes from
Early tests for children divided a “mental age” by the real age and multiplied by 100, which gave a quotient. Adults do not have a mental age that keeps rising, so today’s tests compare people with their own age group instead. The old name stayed.
What IQ tests measure
Most tests combine several kinds of task: reasoning with new problems (fluid reasoning), knowledge and vocabulary (crystallised ability), working memory, processing speed and visual-spatial skills.
Scores on these tasks tend to go together, so researchers summarise them with a general factor, often called g. That is the idea behind a single IQ number.
What IQ does not measure
Creativity, motivation, practical know-how, character and emotional skills are largely outside what IQ tests capture. IQ predicts school results and some job outcomes on average, but it says little about any single person’s life.
Can IQ change?
IQ is fairly stable in adults, but it is not fixed. Schooling, health, nutrition and practice with tests all move scores. Average scores also rose by about three points per decade during the twentieth century in many countries, the so-called Flynn effect.
How to read an online score
Online tests, including ours, give an estimate. A clinical test is given one to one by a psychologist, with norms from thousands of people. Treat any online result as a range, not an exact number.
Questions
What is the average IQ?
By definition, 100. Tests are scaled so that the average of the reference group is exactly 100.
What IQ is considered genius?
There is no scientific threshold. Scores of 140 or more are sometimes called “genius level”, and fewer than 1 in 200 people score that high.
Is IQ inherited?
Partly. Twin studies find that genes explain a large share of the differences between adults in the same environment, but environment matters a lot, especially in childhood.