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An Intelligence quotient, or an IQ is a number. This number is the score of one of several standardized tests, designed to measure the intelligence of an individual. IQ is a comparative measure: it tells one how much above or below the average a person is. The idea of the test is to avoid specific knowledge, and try to ask questions which, in principle, anyone might be able to answer.
German psychologist William Stern in 1912 proposed it as a method of scoring. Intelligence tests for children developed in the early 20th century. Alfred Binet and Théodore Simon proposed this method.
One modern IQ tests is the Wechsler Adult Intelligence Scale. It is based on the subject's rank 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 have an association with other factors, such as mortality, the social status of the parents, and to a big degree, parental IQ. While its inheritance has been investigated for nearly a century, controversy remains as to how much is inheritable, and the mechanisms of inheritance are still a matter of some debate.
IQ scores are used in many contexts: as predictors of educational achievement or special needs, by social scientists who study the distribution of IQ scores in populations and the relationships between IQ score and other variables, and as predictors of job performance and income.
The average IQ scores for many populations have been rising at an average rate of three points per decade since the early 20th century with most of the increase in the lower half of the IQ range: a phenomenon called the Flynn effect. It is disputed whether these changes in scores reflect real changes in intellectual abilities, or merely methodological problems with past or present testing.
General factor (g)[change | edit source]
The many different kinds of IQ tests use a wide variety of methods. Some tests are visual, some are verbal, some tests only use abstract-reasoning problems, and some tests concentrate on arithmetic, spatial imagery, reading, vocabulary, memory or general knowledge. The psychologist Charles Spearman in 1904 made the first formal factor analysis of correlations between the tests. He found a single common factor explained the positive correlations among tests.
This is an argument still accepted in principle by many psychometricians. Spearman named it g for "general factor" and labelled the smaller, specific factors or abilities for specific areas s. In any collection of IQ tests, by definition the test that best measures g is the one that has the highest correlations with all the others. Most of these g-loaded tests typically involve some form of abstract reasoning. Therefore, Spearman and others have regarded g as the (perhaps genetically determined) real essence of intelligence. This is still a common but not universally accepted view. Other factor analyses of the data, with different results, are possible. Some psychometricians regard g as a statistical artifact. One of the most commonly used measures of g is Raven's Progressive Matrices, which is a test of visual reasoning.
The War Years in the United States[change | edit source]
The testing generated controversy and much public debate. Nonverbal or "performance" tests were developed for those who could not speak English or were suspected of malingering. After the war, positive publicity on army psychological testing helped to make psychology a respected field. Subsequently, there was an increase in jobs and funding in psychology in the United States. Group intelligence tests were developed and became widely used in schools and industry.
Problems[change | edit source]
There are a number of problems with intelligence quotients. They relate to different fields of the subject. The problems can be grouped:
- There is no agreement on what intelligence really is. Different branches of science use different definitions. In this context, it is problematic to claim that the intelligence quotient is a measure of intelligence.
- Intelligence may be composed of many different aspects. Some scientist think it is problematic that these different aspects can be combined into one "measurement".
- The first tests were done on children in school, to determine which children would likely need more attention. This is completely different from measuring "intelligence". A child that needs more help in school is not necessarily less intelligent; they might simply come from a different background.
- Some tests require that those tested come from a certain cultural background. People outside the culture will test badly, but they are not necessarily less intelligent.
Test does not measure intelligence[change | edit source]
Alfred Binet, a French psychologist who had designed one of the first such tests in 1905 had this opinion. He used the test to see which pupils would need special help with the school curriculum. He believed that the test scales were not able to measure intelligence:
The scale, properly speaking, does not permit the measure of intelligence, because intellectual qualities are not superposable, and therefore cannot be measured as linear surfaces are measured.—Binet, 1905
He argued that with good education programs, most students could catch up and perform quite well in school. This was independent of the background of the pupil. He did not believe that intelligence was a measurable fixed entity.
Some recent thinkers seem to have given their moral support to these deplorable verdicts by affirming that an individual's intelligence is a fixed quantity, a quantity that cannot be increased. We must protest and react against this brutal pessimism; we must try to demonstrate that it is founded on nothing.
Some scientists dispute psychometrics entirely. Harvard professor and paleontologist Stephen Jay Gould argued that intelligence tests were based on faulty assumptions and showed their history of being used as the basis for scientific racism. He wrote:
…the abstraction of intelligence as a single entity, its location within the brain, its quantification as one number for each individual, and the use of these numbers to rank people in a single series of worthiness, invariably to find that oppressed and disadvantaged groups—races, classes, or sexes—are innately inferior and deserve their status.(pp. 24–25)
In his opinion, the General intelligence factor g (which these tests measure), is simply a mathematical artifact.
The relation between IQ and intelligence is unclear[change | edit source]
- See also: Intelligence
According to Dr. C. George Boeree of Shippensburg University, intelligence is a person's capacity to (1) acquire knowledge (i.e. learn and understand), (2) apply knowledge (solve problems), and (3) engage in abstract reasoning. It is the power of one's intellect, and as such is clearly a very important aspect of one's overall well-being. Psychologists have attempted to measure it for well over a century.
Several other ways of measuring intelligence have been proposed. Daniel Schacter, Daniel Gilbert, and others have moved beyond general intelligence and IQ as the sole means to describe intelligence.
Tests are biased or use old methods[change | edit source]
The American Psychological Association's report Intelligence: Knowns and Unknowns states that IQ tests as predictors of social achievement are not biased against people of African descent since they predict future performance, such as school achievement, similarly to the way they predict future performance for European descent.
However, IQ tests may well be biased when used in other situations. A 2005 study stated that "differential validity in prediction suggests that the WAIS-R test may contain cultural influences that reduce the validity of the WAIS-R as a measure of cognitive ability for Mexican American students," indicating a weaker positive correlation relative to sampled white students. Other recent studies have questioned the culture-fairness of IQ tests when used in South Africa. Standard intelligence tests, such as the Stanford-Binet, are often inappropriate for children with autism and dyslexia; the alternative of using developmental or adaptive skills measures are relatively poor measures of intelligence in autistic children, and have resulted in incorrect claims that a majority of children with autism are mentally retarded.
A 2006 paper argues that mainstream contemporary test analysis does not reflect substantial recent developments in the field and "bears an uncanny resemblance to the psychometric state of the art as it existed in the 1950s." It also claims that some of the most influential recent studies on group differences in intelligence, in order to show that the tests are unbiased, use outdated methodology.
Claimed low intelligence has historically been used to justify the feudal system and unequal treatment of women (see sex and intelligence). In contrast, others claim that the refusal of "high-IQ elites" to take IQ seriously as a cause of inequality is itself immoral.
The view of the American Psychological Association[change | edit source]
In response to the controversy surrounding The Bell Curve, the American Psychological Association's Board of Scientific Affairs established a task force in 1995 to write a consensus statement on the state of intelligence research which could be used by all sides as a basis for discussion. The full text of the report is available through several websites.
In this paper the representatives of the association regret that IQ-related works are frequently written with a view to their political consequences: "research findings were often assessed not so much on their merits or their scientific standing as on their supposed political implications".
The task force concluded that IQ scores do have high predictive validity for individual differences in school achievement. They confirm the predictive validity of IQ for adult occupational status, even when variables such as education and family background have been statistically controlled. They found that individual differences in intelligence are substantially influenced by genetics and that both genes and environment, in complex interplay, are essential to the development of intellectual competence.
They state there is little evidence to show that childhood diet influences intelligence except in cases of severe malnutrition. The task force agrees that large differences do exist between the average IQ scores of blacks and whites, and that these differences cannot be attributed to biases in test construction. The task force suggests that explanations based on social status and cultural differences are possible, and that environmental factors have raised mean test scores in many populations. Regarding genetic causes, they noted that there is not much direct evidence on this point, but what little there is fails to support the genetic hypothesis..
The APA journal that published the statement, American Psychologist, subsequently published eleven critical responses in January 1997, several of them arguing that the report failed to examine adequately the evidence for partly-genetic explanations.
References[change | edit source]
- Indiana University (2007). "William Stern". Indiana University. http://www.indiana.edu/~intell/stern.shtml. Retrieved July 15 2009.
- i.e. as a quotient of "mental age" and "chronological age."
- Cervilla et al. (2004). "Premorbid cognitive testing predicts the onset of dementia and Alzheimer's disease better than and independently of APOE genotype". Psychiatry 2004;75:1100-1106.. http://www.jnnp.com/cgi/content/abstract/75/8/1100. Retrieved August 6 2006.
- 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, Feb 1996. Official Journal of the APA)
- Devlin B, Daniels M, Roeder K (1997). "The heritability of IQ". Nature 388 (6641): 468–71. doi:10.1038/41319. PMID 9242404.
The same study suggests that the heritable component of IQ becomes more significant with age.
- Neisser U (1997). "Rising Scores on Intelligence Tests". American Scientist 85: 440–7. http://www.americanscientist.org/issues/feature/rising-scores-on-intelligence-tests/1.
- Kaufman, Alan S. 2009. IQ Testing 101. New York: Springer. ISBN 978-0-8261-0629-2
- Kennedy, Carrie H.; McNeil, Jeffrey A. (2006). "A history of military psychology". In Kennedy, Carrie H.; Zillmer, Eric. Military Psychology: Clinical and Operational Applications. New York: Guilford Press. pp. 1–17. ISBN 1-57230-724-2. http://books.google.com/books?id=rytCzdXGgXkC&pg=PA1.
- Katzell, Raymond A.; Austin, James T. (1992). "From then to now: The development of industrial-organizational psychology in the United States". Journal of Applied Psychology 77 (6): 803–35. doi:10.1037/0021-9010.77.6.803.
- Kevles, D. J. (1968). "Testing the Army's Intelligence: Psychologists and the Military in World War I". The Journal of American History 55 (3): 565–81. doi:10.2307/1891014.
- Rawat, R. The Return of Determinism?
- The Waning of I.Q. by David Brooks, The New York Times
- Neisser et al. (August 7, 1995). "Intelligence: Knowns and Unknowns". Board of Scientific Affairs of the American Psychological Association. http://www.lrainc.com/swtaboo/taboos/apa_01.html. Retrieved August 6 2006.
- Culture-Fair Cognitive Ability Assessment Steven P. Verney Assessment, Vol. 12, No. 3, 303-319 (2005)
- Shuttleworth-Edwards AB, Kemp RD, Rust AL, Muirhead JG, Hartman NP, Radloff SE (2004). "Cross-cultural effects on IQ test performance: a review and preliminary normative indications on WAIS-III test performance". J Clin Exp Neuropsychol 26 (7): 903–920. doi:10.1080/13803390490510824. PMID 15742541.
- Case for Non-Biased Intelligence Testing Against Black Africans Has Not Been Made: A Comment on Rushton, Skuy, and Bons (2004) 1*, Leah K. Hamilton1, Betty R. Onyura1 and Andrew S. Winston International Journal of Selection and Assessment Volume 14 Issue 3 Page 278 - September 2006
- Edelson, MG (2006). "Are the majority of children with autism mentally retarded? a systematic evaluation of the data". Focus Autism Other Dev Disabl 21 (2): 66–83. doi:10.1177/10883576060210020301. http://www.willamette.edu/dept/comm/reprint/edelson/. Retrieved 2007-04-15.
- The attack of the psychometricians. Denny Borsboom. Psychometrika Vol. 71, No. 3, 425–440. September 2006.
- Steve Sailer (2000). "How to Help the Left Half of the Bell Curve". VDARE.com. http://www.isteve.com/How_to_Help_the_Left_Half_of_the_Bell_Curve.htm. Retrieved 2006-08-06.
- World Intelligence Network, IQ & Genetics
- Gosso, MF (2006). "The SNAP-25 gene is associated with cognitive ability: evidence from a family-based study in two independent Dutch cohorts". Molecular Psychiatry 11 (9): 878-886. doi:10.1038/sj.mp.4001868.
- Gosso MF, de Geus EJ, van Belzen MJ, Polderman TJ, Heutink P, Boomsma DI, Posthuma D. The SNAP-25 gene is associated with cognitive ability: evidence from a family-based study in two independent Dutch cohorts