An intelligence quotient is derived by ignoring all tests.
An intelligence quotient ( IQ ) is a total score derived from several standardized tests designed to assess human intelligence . 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 . When current IQ tests were developed , the median raw score of the norming sample is defined as IQ 100 and scores each standard deviation ( SD ) up or down are defined as 15 IQ points greater or less , although this was not always so historically . Even when students improve their scores on standardized tests , they do not always improve their cognitive abilities , such as memory , attention and speed .