IQ was originally computed as the ratio of a person's mental age to his or her chronological physical age, multiplied by 100, but use of the concept of mental age has been largely discontinued, and IQ is now generally assessed on the basis of the statistical distribution of scores.  The most widely used intellegence tests are the Stanford-Binet test (1916), for children, and the Wechsler test (1939), originally for adults but also now for children.  A score above 130 is considered to reflect "giftedness", while a score below 70 is considered to relect mental impairment.  Intelligence tests have provoked great controversy, particularly about what kinds of mental ability constitute intelligence and whether IQ adequately represents these abilities, and about cultural and class bias in test construction and standardization prodcedures.