Intelligence quotient

An intelligence quotient (acronym: IQ) is a number. This number is the score (result) of a standard test to measure intelligence. There are several different tests designed to measure the intelligence of a person. Measuring intelligence in any way is an idea developed by British scientist Francis Galton in the book Hereditary genius published in the late 19th century.

IQ is a comparative measure: it tells one how much above or below the average a person is.^[1] The idea of the test was developed at the start of the 20th century.^[2][3] The tests try to avoid specific knowledge, and try to ask questions which, in principle, anyone should be able to answer.

One modern IQ test is the Wechsler Adult Intelligence Scale. It says where the subject's score is on the Gaussian bell. The bell curve used has a center value of 100 and a standard deviation of 15; other tests may have different standard deviations.

IQ scores can tell some things about a person, as well as intelligence. This is because intelligence is linked to other aspects of life. "All the cognitive tests completed in 1983 predicted onset of dementia and Alzheimer’s disease up to 11 years later".^[4] They can predict the social status of the parents,^[5] and the parents' IQ.

There is still disagreement about to what extent IQ is inherited. People still disagree about how much of a person's IQ comes from parents and how much depends on their environment (what their home is like).^[6][7]

IQ scores are used in various ways:

1. to predict a person's educational achievement or special needs.
2. to study what the IQ scores of a population are like.
3. to study what other things about a person are related to his/her IQ.
4. in the past, they have been used to find out which jobs a person might be able to do.

The average IQ scores for many populations have been rising about three points per decade since the early 20th century. Most of the increase is in the lower half of the IQ range. This is called the Flynn effect. People who study it disagree whether these changes in scores are really happening, or it they mean that there were mistakes in how people were tested in the past.

There are associations of people who have scored high on IQ tests, such as Mensa International.

1. ↑ By 'average' is meant the median.
2. ↑ Indiana University (2007). "William Stern". Indiana University. Archived from the original on 2013-09-26. Retrieved 2009-10-24.
3. ↑ i.e. as a quotient of "mental age" and "chronological age."
4. ↑ Cervilla A. Psychiatry 75:1100-1106. (2004). "Premorbid cognitive testing predicts the onset of dementia and Alzheimer's disease better than and independently of APOE genotype".{{cite web}}: CS1 maint: numeric names: authors list (link)
5. ↑ Intelligence: knowns and unknowns Report of a Task Force established by the Board of Scientific Affairs of the American Psychological Association - Released August 7, 1995 - A slightly edited version was published in the American Psychologist, February 1996. Official Journal of the APA
6. ↑ Bouchard T.J. Jr & McGue M. 1981. Familial studies of intelligence: a review. Science 212: 1055–1059.
7. ↑ Devlin B. Daniels M. & Roeder K. (1997). "The heritability of IQ". Nature. 388 (6641): 468–71. Bibcode:1997Natur.388..468D. doi:10.1038/41319. PMID 9242404. S2CID 4313884.
   The same study suggests that the heritable component of IQ becomes more significant with age.