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IQ

(Redirected from Intelligence Quotient)

IQ, an abbreviation for "intelligence quotient", is a score derived from a set of standardized tests that were developed with the purpose of measuring a person's cognitive abilities ("intelligence") in relation to their age group. It is expressed as a number normalized so that the average IQ in an age group is 100 — in other words an individual scoring 115 is above-average when compared to similarly aged people. It is common, but not invariable, practice to standardise so that the standard deviation (σ) of scores is 15. Tests are designed so that the distribution of IQ scores is more-or-less Gaussian, that is to say that it follows a bell curve.

Contents

Introduction

IQ scores are generally taken as an objective measure of intelligence. See the Intelligence (trait) entry for an in-depth discussion of the controversies regarding definition and measurability of intelligence.

Modern IQ tests produce scores for different areas (e.g., language fluency, three-dimensional thinking, etc.), with the summary score calculated from subtest scores. Individual subtest scores tend to correlate with one another, even when seemingly disparate in content. Analyses of an individual's scores on a wide variety of tests will reveal that they all measure a single common factor and various factors that are specific to each test. This kind of analysis has led to the theory that underlying these disparate cognitive tasks is a single factor, termed the g factor, that represents the common-sense concept of intelligence. In the normal population, g and IQ are roughly 90% correlated and are often used interchangeably.

Some argue that IQ tests encode their creator's beliefs about what constitutes intelligence. There is little empirical support for this perspective, at least as it applies to validated IQ tests (Stanford-Binet, WISC-R, Raven's Progressive Matrices and others). The statistical extraction of g from batteries of cognitive tests via factor analysis has proven highly reliable in producing the same g from diverse tests, suggesting that creators have little ability to determine the outcome of valid cognitive tests. Unvalidated tests (see Online IQ tests, below) may not have the same level of reliability.

(The following numbers apply to IQ scales with a standard deviation σ = 15.) Roughly 68% of the population has an IQ between 85 and 115. The "normal" range, or range between -2 and +2 standard deviations from the mean, is between 70 and 130, and contains about 95% of the population. A score below 70 may indicate mental retardation, and a score above 130 may indicate intellectual giftedness. Retardation may result from normal variation or from a genetic or developmental malady; analogously, some otherwise normal people are very short, and others have dwarfism. Giftedness appears to be normal variation; autistic savants have often astonishing cognitive powers but below-average IQs.

Some writers say that scores outside the range 55 to 145 must be cautiously interpreted because there have not been enough people tested in those ranges to make statistically sound statements. Moreover, at such extreme values, the normal distribution is a less accurate estimate of the IQ distribution.

Scores on a given test in a given population have tended to rise across time throughout the history of IQ testing (the Flynn effect), so that tests need repeated renormalization.

History

The modern field of IQ testing began with the Stanford-Binet test. Alfred Binet, who created the IQ test in 1904, aimed to identify students who could benefit from extra help in school; his assumption was that lower IQ indicated the need for more teaching, not an inability to learn. This interpretation is still held by some modern experts. The term "intelligence quotient" comes from Binet's test, in which each student's score was the quotient of his or her tested academic age with his or her actual age. Modern IQ tests do not calculate scores in this way, but the term IQ remains in common use.

Gender and IQ

Most IQ tests are designed so that the average IQs of males and females are equal. However, men tend to score higher in the parts of the test that cover spatial and quantitative abilities, and women generally score higher in the verbal sections. Some research has shown that the variance in men's IQ scores is greater than the variance among women's, as seen in other cognitive test scores. This is why more men than women are found in both very high and very low scoring groups.

Race and IQ

See main article: Race and intelligence

Opposition to IQ testing

Many scientists disagree with the practice of psychometrics in general. In The Mismeasure of Man, Professor Stephen Jay Gould strongly disputes the basis of psychometrics as a form of scientific racism, objecting that it is:

...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).

Later editions of the book include a refutation of The Bell Curve.

While public discourse on IQ testing is generally inflammatory, IQ tests are used ubiquitously in research and education. In general, there is a disparity between the public perception of IQ testing and the opinion of intelligence researchers.

Some proponents of IQ have pointed to a number of studies showing a fairly close correlation between IQ and various life outcomes, particularly income. Research in Scotland http://news.bbc.co.uk/hi/english/health/newsid_1260000/1260794.stm has shown that a 15-point lower IQ meant people had a fifth less chance of seeing their 76th birthday, while those with a 30-point disadvantage were 37% less likely than those with a higher IQ to live that long. Research by Charles Murray on siblings http://www.eugenics.net/papers/murray.html has shown that there is a strong correlation between IQ and earned income. A controversial book by Richard Lynn, IQ and the Wealth of Nations, claims to show that the wealth of a nation correlates closely to its IQ score.

The reduction of intelligence to a single score seems extreme and wrong to many people. Opponents argue that it is much more useful to know a person's strengths and weaknesses than to know their IQ score. Such opponents often cite the example of two people with the same overall IQ score but very different ability profiles. However, most people have highly balanced ability profiles. Differences in subscores are greatest among the most intelligent, which may lead them to this misconception. For certain areas, such as academic achievement and job performance, an IQ score is the best-known single predictor of success, though other factors add small amounts to the predictive validity (see Intelligence (trait) for a more in-depth discussion).

IQ scores are not intended to gauge a person's worth, and in many situations, IQ may have little relevance.

SAT

The SAT measures IQ to a significant degree according to a recent study (Frey and Detterman, 2003). The study's authors provide methods for estimating IQ scores from SAT scores. Mensa, a high IQ society, accepts individuals who scored at the 98th percentile, or 1300+ on tests scored prior to 30 September 1974, and 1250+ on tests scored after that date through 31 January 1994. After the test was recentered in 1995, Mensa decided that the SAT was no longer an IQ test and does not accept SAT scores of 1300+ (renormed 98th percentile) from 1995 onward for admission. However, tables to correlate (both historical and modern) SAT scores to IQ do exist, and can be found here. http://members.shaw.ca/delajara/GREIQ.html

Online IQ tests

Although such tests have become wildly popular with the explosion of the Internet in recent years, there is great reason to believe that these IQ tests are highly inaccurate in their estimation of one's IQ. For example, by inputting random answers on one particular IQ test, an IQ of roughly 80 is obtained. Comparing results among a large set of people shows a common factor—most scores are above 110. Most of these websites attempt to sell certificates showing test results. It is therefore recommended not to take online IQ tests as a true judge of one's IQ.

References

  • Frey, M.C. and Detterman, D.K. (2003) Scholastic Assessment or g? The Relationship Between the Scholastic Assessment Test and General Cognitive Ability. Psychological Science, 15(6):373-378. PDF http://www.gnxp.com/MT2/archives/2003_frey_and_detterman_IQ_SAT.pdf
  • Jensen, A.R. (1998). The g Factor. Praeger, Connecticut, USA.

See also

External links

  • Estimated IQs of the greatest geniuses http://hem.bredband.net/b153434/Index.htm
  • Number of highly gifted relatives of high IQ people http://www.volkmar-weiss.de/table.html
  • Scientific American: Intelligence Considered http://www.psych.utoronto.ca/~reingold/courses/intelligence/cache/1198yam.html
  • Scientific American: The General Intelligence Factor http://www.psych.utoronto.ca/~reingold/courses/intelligence/cache/1198gottfred.h
    tml
  • The Basic Period of Individual Mental Speed, Underlying IQ http://www.volkmar-weiss.de/lehrl.html
  • Uncommonly difficult IQ tests http://www.eskimo.com/~miyaguch/hoeflin.html
  • Wall Street Journal: Mainstream Science on Intelligence http://www.lrainc.com/swtaboo/taboos/wsj_main.html
  • Sex differences in the brain http://www.sciam.com/article.cfm?articleID=00018E9D-879D-1D06-8E49809EC588EEDF
  • High range IQ tests and societies http://members.chello.nl/p.cooijmans/gliaweb/



Last updated: 03-18-2005 11:16:12