An
intelligence quotient (
IQ) is a score derived from one of 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 he advocated in a 1912 book. When current IQ tests are 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. By this definition, approximately two-thirds of the population scores between IQ 85 and IQ 115. About 5 percent of the population scores above 125, and 5 percent below 75.