IQ, or intelligence quotient, is a number determined by a person's performance on a standardized test designed to measure IQ; these tests may include the Stanford-Binet Intelligence Scales, the Wechsler Adult Intelligence Scale or the Wechsler Intelligence Scale for Children. In some cases, different IQ tests can produce different results, and critics of these tests have argued that these tests are biased toward certain races, genders and social classes. In most cases, the IQ is determined by dividing the "mental age" determined by the test with the test-taker's real age, meaning that though intelligence tends to increase as people age, their increasing age will factor into the equation, leading to relatively stable IQ through time.
Most normally intelligent people who take an IQ test will end up with a score in the range of 70 to 130. Only about 5 percent of IQ test takers end up outside of that range. However, there is an observed phenomenon known as the Flynn effect that relates to the fact that IQ scores are rising in time. On average, IQ scores are rising about three points per decade, meaning younger people tend to test a bit higher on the test than older people. One's performance on an IQ test may depend on factors other than raw intelligence as different tests focus on different skills.