Intelligence quotient
Atomic claims
An intelligence quotient (IQ) is a standardized score derived from psychometric tests.
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Psychometric tests used for IQ are designed to assess human cognitive ability relative to a reference population.
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Modern intelligence tests report a 'deviation IQ'.
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Modern deviation IQ scores are scaled to a mean of 100.
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IQ scores predict several educational outcomes.
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The interpretation of what IQ scores measure remains debated.
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The causes of individual and group differences in IQ scores remain debated.
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Alfred Binet and Théodore Simon published the first practical intelligence scale in 1905.
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The 1905 Binet-Simon intelligence scale was commissioned to identify French schoolchildren needing special instruction.
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William Stern introduced the term 'Intelligenzquotient' in 1912.
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William Stern defined 'Intelligenzquotient' as mental age divided by chronological age.
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Lewis Terman published the Stanford-Binet revision in 1916.
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David Wechsler published the Wechsler-Bellevue scale in 1939.
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The 1939 Wechsler-Bellevue scale replaced the ratio IQ with a deviation score based on the test-taker's position in an age-group distribution.
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Current Wechsler scales use a mean of 100 and a standard deviation of 15.
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Under a normal distribution with a mean of 100 and standard deviation of 15, about 68% of IQ scores fall between 85 and 115.
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Charles Spearman reported in 1904 that scores on diverse cognitive tasks correlate positively.
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Charles Spearman proposed a general factor, g, for cognitive tasks.
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John Carroll conducted a factor-analytic survey of over 400 datasets in 1993.
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The Cattell-Horn-Carroll model organizes cognitive abilities hierarchically with broad abilities beneath a general factor.
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An American Psychological Association task force concluded in 1996 that IQ scores correlate about 0.50 with school grades.
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Meta-analytic work by Schmidt and Hunter reported general mental ability as among the strongest single predictors of job performance.
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Later reanalysis of Schmidt and Hunter's work revised the estimated validity of general mental ability as a predictor of job performance downward.
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Twin and adoption studies estimate the heritability of IQ rises with age.
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Genome-wide association studies have identified many loci associated with intelligence.
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The individual genomic loci associated with intelligence each have a very small effect.
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A 2018 meta-analysis of about 270,000 individuals identified 205 genomic loci associated with intelligence.
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Average raw intelligence test performance rose substantially across the 20th century in many countries.
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The Flynn effect is estimated at an order of 3 IQ points per decade.
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Declines or stagnation in IQ scores have been reported in some countries since the 1990s.
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A Norwegian study found that the reversal of the Flynn effect occurs within families.
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The within-family reversal of IQ scores indicates environmental causes.
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A meta-analysis estimated that each additional year of education raises IQ by approximately 1 to 5 points.
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Childhood IQ is associated with later mortality risk.
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Cohort studies show that lower childhood IQ scores predict earlier death.
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In Atkins v. Virginia (2002), the US Supreme Court barred the execution of people with intellectual disability.
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In Hall v. Florida (2014), the US Supreme Court rejected a rigid IQ cutoff of 70 for determining intellectual disability.
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The DSM-5 defines intellectual disability by deficits in both intellectual and adaptive functioning.
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The DSM-5 does not define intellectual disability by IQ score alone.
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Early IQ testing was used in support of eugenic policies in the United States in the early 20th century.
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The extent of the direct influence of early IQ testing on the 1924 Immigration Act is disputed by historians.
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IQ test scores intercorrelate.
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IQ test scores yield a general factor.
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It is unresolved whether the general factor (g) reflects a unitary causal property or emerges from interacting processes.
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The mutualism model posits that the general factor emerges from interacting processes.
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Howard Gardner proposed a framework of multiple intelligences in 1983.
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Robert Sternberg proposed the triarchic theory of intelligence in 1985.
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Alternative intelligence frameworks like Gardner's multiple intelligences and Sternberg's triarchic theory have been criticized for limited psychometric support.
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Average IQ score differences between some racial, ethnic, and national groups are documented.
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The 1996 APA task force stated there was no direct empirical support for a genetic explanation of group IQ differences.
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The 1996 APA task force stated that the causes of group IQ differences were unknown.
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Nisbett et al. argued in 2012 that evidence favors environmental explanations for group IQ differences.
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A minority of researchers have argued for a partial genetic contribution to group IQ differences.
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Heritability is a population statistic.
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Heritability does not indicate immutability.
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Heritability does not apply to between-group differences.
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Turkheimer et al. reported in 2003 that IQ heritability is lower in low-socioeconomic-status US families.
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Replication of Turkheimer et al.'s findings on socioeconomic status and IQ heritability has been inconsistent across countries.
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The 1996 APA task force found that IQ tests are not biased in the predictive sense against US minority groups.
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Critics argue that cultural loading and unequal opportunity affect what IQ scores mean.
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Proposed explanations for the Flynn effect include nutrition, schooling, test familiarity, and smaller family size.
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There is a lack of consensus on the causes of the Flynn effect.
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Psychometric tests from which an IQ is derived are designed to measure human cognitive abilities.
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Modern IQ tests are statistically normed so that the median score of the general population is exactly 100.
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Modern IQ tests are statistically normed with a set standard deviation.
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IQ scores are widely used in educational placement.
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The application of IQ scores remains a subject of scientific and public debate.
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The term "intelligence quotient" originally referred to a score calculated by dividing an individual's assessed "mental age" by their chronological age, and multiplying the result by 100.
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Modern IQ tests utilize "deviation IQ" scoring rather than age ratios.
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"Deviation IQ" scoring anchors the median raw score of the norming sample to a defined population mean of exactly 100.
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The standard deviation for most contemporary IQ tests is mathematically set at 15 points.
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IQ scores are scaled to a normal distribution (bell curve).
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Approximately 68% of the population scores between 85 and 115 on scaled IQ tests.
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The Wechsler Adult Intelligence Scale (WAIS) is among the most frequently administered contemporary IQ assessments.
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Major contemporary IQ tests demonstrate high statistical reliability.
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Major contemporary IQ tests frequently show reliability coefficients above 0.90.
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Reliability coefficients above 0.90 indicate that test-takers achieve consistent scores across repeated administrations.
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IQ scores demonstrate predictive validity for specific life outcomes.
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IQ scores most notably correlate with academic achievement and school performance.
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Behavioral genetics research indicates that intelligence, as measured by IQ, is highly heritable.
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Behavioral genetics research estimates that the genetic contribution to intelligence differences increases from childhood into adulthood.
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The "Flynn effect" refers to the phenomenon of substantial and long-sustained increases in intelligence test scores measured in many parts of the world over the 20th century.
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The "Flynn effect" encompasses increases in both fluid and crystallized intelligence test scores.
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Researchers estimate the rate of the Flynn effect at approximately 3 points per decade throughout much of the 20th century.
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Researchers generally attribute the rise in IQ scores over the 20th century to environmental factors.
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Critics and theorists, such as Robert Sternberg and Howard Gardner, argue that IQ tests measure a narrow slice of human cognitive ability (such as logical-mathematical and linguistic skills).
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Critics and theorists argue that IQ tests neglect other critical dimensions like creative, practical, or emotional intelligence.
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The extent to which IQ tests contain cultural biases that favor certain socioeconomic or ethnic groups over others is heavily debated.
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Psychometricians have attempted to eliminate culturally loaded questions from IQ tests.
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Critics argue that the underlying construct of intelligence being tested in IQ tests reflects specific cultural values rather than an innate, universal cognitive capacity.
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The observation of mean IQ score differences between various racial and ethnic groups is highly contentious.
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A minority of researchers have posited partial genetic explanations for mean IQ score differences between various racial and ethnic groups.
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Mainstream psychological and anthropological consensus emphasizes that mean IQ score differences between various racial and ethnic groups are driven by complex environmental variables.
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Mainstream consensus emphasizes that environmental variables driving group IQ differences include socioeconomic status, educational access, systemic discrimination, and the Flynn effect.
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External references: Wikidata Q170277