<P> Mental age was first defined by the French psychologist Alfred Binet, who introduced the intelligence test in 1905, with the assistance of Theodore Simon . Binet's experiments on French schoolchildren laid the framework for future experiments into the mind throughout the Twentieth Century . He created an experiment that was designed as a test to be completed quickly and was taken by various ages of children . As was expected, the older children performed better on these tests . However, the younger children who had exceeded the average of their peers were said to have a higher "mental age" and those who performed below average were deemed to have a lower mental age . Binet's theories suggested that while mental age was a useful indicator, it was by no means permanently affixed and individual growth or decline could be attributed to changes in teaching methods and experiences . </P> <P> Henry Herbert Goddard was the first psychologist to bring Binet's test to the United States . Goddard was amongst one of the many psychologists in the 1910s that believed intelligence was a fixed quantity . While Binet believed this wasn't the case, the majority of those in the U.S believed it was hereditary . </P> <P> The limitations of the Stanford - Binet caused David Wechsler to publish the Wechsler Adult Intelligence Scale (WAIS) in 1955 . These two tests were split into two different ones for children . The WAIS - IV is the known current publication of the test for adults . The reason for this test was to score the individual and compare it to others of the same age group rather than to score by chronological age and mental age . The fixed average is 100 and the normal range is between 85 and 115 . This is a standard currently used and is used in the Stanford - Binet test as well . </P> <P> Originally, the differences between mental age and chronological age were used to compute the intelligence quotient, or IQ . This was computed using the ratio method, with the following formula: </P>

The ratio iq is calculated by the formula