Claim: Intelligence quotient scores are estimates of intelligence as concrete measures are impossible.

An intelligence quotient -LRB- IQ -RRB- is a total score derived from several standardized tests designed to assess human intelligence . The abbreviation `` IQ '' was coined by the psychologist William Stern for the German term Intelligenzquotient , his term for a scoring method for intelligence tests at University of Wrocław he advocated in a 1912 book . Historically , IQ is a score obtained by dividing a person 's mental age score , obtained by administering an intelligence test , by the person 's chronological age , both expressed in terms of years and months . The resulting fraction is multiplied by 100 to obtain the IQ score . When current IQ tests were developed , the median raw score of the norming sample is defined as IQ 100 and scores each standard deviation -LRB- SD -RRB- up or down are defined as 15 IQ points greater or less , although this was not always so historically . By this definition , approximately two-thirds of the population scores are between IQ 85 and IQ 115 . About 5 percent of the population scores above 125 , and 5 percent below 75 .   Scores from intelligence tests are estimates of intelligence because concrete measurements -LRB- e.g. distance , mass -RRB- can not be achieved given the abstract nature of the concept of `` intelligence '' . IQ scores have been shown to be associated with such factors as morbidity and mortality , parental social status , and , to a substantial degree , biological parental IQ . While the heritability of IQ has been investigated for nearly a century , there is still debate about the significance of heritability estimates and the mechanisms of inheritance .   IQ scores are used for educational placement , assessment of intellectual disability , and evaluating job applicants . Even when students improve their scores on standardized tests , they do not always improve their cognitive abilities , such as memory , attention and speed . In research contexts they have been studied as predictors of job performance , and income . They are also used to study distributions of psychometric intelligence in populations and the correlations between it and other variables . Raw scores on IQ tests for many populations have been rising at an average rate that scales to three IQ points per decade since the early 20th century , a phenomenon called the Flynn effect . Investigation of different patterns of increases in subtest scores can also inform current research on human intelligence .