In 1905, the French psychologists Alfred Binet and Théodore Simon proposed the concept of an intelligence test that measured mental age. In 1912, the German psychologist William Stern proposed the division of mental age by chronological age, to give the intelligence quotient. In 1916 the test was introduced into the USA by Lewis Terman of Stanford U. Terman proposed scaling the quotient by 100, to remove awkward decimal places, and as a result the test became known as the Stanford–Binet test. The idea of a mental age to chronological age ratio only works well for the young, however. As a consequence the original ratio concept has been abandoned. In 1939 the Romanian-born US psychologist David Wechsler introduced a statistical definition of IQ as a random variable having a normal distribution with mean 100 and standard deviation 15, so that most people then have IQs in the range 70 to 130, with IQs over 150 being extremely rare.