Intelligence quotient
Diagnostics
An example of one kind of IQ test item, modeled after items in the Raven's Progressive Matrices test.
ICD-9-CM	94.01

An intelligence quotient, or IQ, is a score derived from one of several standardized tests designed to assess intelligence. The abbreviation "IQ" comes from the German term Intelligenz-Quotient, originally coined by psychologist William Stern. When modern IQ tests are devised, the mean (average) score within an age group is set to 100 and the standard deviation (SD) almost always to 15, although this was not always so historically.^[1] Thus the intention is that approximately 95% of the population scores within two SDs of the mean, i.e. has an IQ between 70 and 130.

IQ scores have been shown to be associated with such factors as morbidity and mortality^[2], parental social status,^[3] and, to a substantial degree, parental IQ. While the heritability of IQ has been investigated for nearly a century, there is still debate about the significance of heritability estimates^[4][5] and the mechanisms of inheritance.^[6]

IQ scores are used as predictors of educational achievement, special needs, job performance and income. They are also used to study IQ distributions in populations and the relationships between IQ and other variables. The average IQ scores for many populations have been rising at an average rate of three points per decade since the early 20th century, a phenomenon called the Flynn effect. It is disputed whether these changes in scores reflect real changes in intellectual abilities.

Whether IQ tests are an accurate measure of intelligence is debated. It is difficult to define what constitutes intelligence; instead it may be the case that IQ represents a type of intelligence.

History[link]

Early history[link]

The first large scale mental test may have been the imperial examination system in China. Modern mental testing began in France in the nineteenth century. It contributed to separating mental retardation from mental illness and reducing the neglect, torture, and ridicule heaped on both groups.^[7]

Englishman Francis Galton coined the terms psychometrics and eugenics, and developed a method for measuring intelligence based on nonverbal sensory-motor tests. It was initially popular but was abandoned after the discovery that it had no relationship to outcomes such as college grades.^[7][8]

French psychologist Alfred Binet, together with psychologists Victor Henri and Théodore Simon, after about 15 years of development, published the Binet-Simon test in 1905 which focused on verbal abilities. It was intended to identify mental retardation in school children.^[7] The score on the Binet-Simon scale would reveal the child's mental age. For example, a 6 year-old child who passed all the tasks usually passed by 6 year-olds—but nothing beyond—would have a mental age that exactly matched his chronological age, 6.0. (Fancher, 1985). In Binet's view there were limitations with the scale and he stressed what he saw as the remarkable diversity of intelligence and the subsequent need to study it using qualitative, as opposed to quantitative, measures (White, 2000). American psychologist Henry H. Goddard published a translation of it in 1910. The eugenics movement in the USA seized on it as a means to give them credibility in diagnosing mental retardation, and thousands of American women, most of them poor African-Americans, were forcibly sterilized based on their scores on IQ tests, often without their consent or knowledge.^[9] American psychologist Lewis Terman at Stanford University revised the Binet-Simon scale which resulted in the Stanford-Binet Intelligence Scales (1916). It became the most popular test in the United States for decades.^{[7][10][11][12]}

[edit] General factor (g)

There are many different kinds of IQ tests using 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 that 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 best measures of g is Raven's Progressive Matrices which is a test of visual reasoning.^[1][7]

The War Years[link]

During World War I, a way was needed to evaluate and assign recruits. This led to the rapid development of several mental tests. 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.^[7] After the war, positive publicity on army psychological testing helped to make psychology a respected field.^[13] Subsequently there was an increase in jobs and funding in psychology.^[14] Group intelligence tests were developed and became widely used in schools and industry.^[15]

L.L. Thurstone argued for a model of intelligence that included seven unrelated factors (verbal comprehension, word fluency, number facility, spatial visualization, associative memory, perceptual speed, reasoning, and induction). While not widely used, it influenced later theories.^[7]

David Wechsler produced the first version of his test in 1939. It gradually became more popular and overtook the Binet in the 1960s. It has been revised several times, as is common for IQ tests in order to incorporate new research. One explanation is that psychologists and educators wanted more information than the single score from the Binet. Wechsler's 10+ subtests provided this. Another is Binet focused on verbal abilities while the Wechsler also included non-verbal abilities. The Binet has also been revised several times and is now similar to the Wechsler in several aspects but the Wechsler continues to be the most popular test in the United States.^[7]

Cattell-Horn-Carroll theory[link]

Raymond Cattell (1941) proposed two types of cognitive abilities in a revision of Spearman's concept of general intelligence. Fluid intelligence (Gf) was hypothesized as the ability to solve novel problems by using reasoning and crystallized intelligence (Gc) was hypothesized as a knowledge-based ability that was very dependent on education and experience. In addition, fluid intelligence was hypothesized to decline with age while crystallized intelligence was largely resistant. The theory was almost forgotten but revived by his student John L. Horn (1966) who later argued that Gf and Gc were only two among several factors and he eventually identified 9 or 10 broad abilities. The theory continued to be called Gf-Gc theory.^[7]

John B. Carroll (1993) after a comprehensive re-analysis of earlier data proposed the Three Stratum Theory, which is a hierarchical model with three levels. At the bottom is the first stratum which consists of narrow abilities that are highly specialized (e.g., induction, spelling ability). The second stratum consists of broad abilities. Carroll identified eight second-stratum abilities. Carroll accepted Spearman's concept of general intelligence, for the most part, as a representation of the uppermost third stratum.^[16][17]

More recently (1999), a merging of the Gf-Gc theory of Cattell and Horn with Carroll's Three-Stratum theory has led to the Cattell-Horn-Carroll theory. It has greatly influenced many of the current IQ tests.^[7]

Many of the broad, recent IQ tests have been greatly influenced by the Cattell-Horn-Carroll theory. It is argued to reflect much of what is known about intelligence from research. A hierarchy of factors is used. g is at the top. Under it there are 10 broad abilities that in turn are subdivided into 70 narrow abilities. The broad abilities are:^[7]

• Fluid Intelligence (Gf): includes the broad ability to reason, form concepts, and solve problems using unfamiliar information or novel procedures.
• Crystallized Intelligence (Gc): includes the breadth and depth of a person's acquired knowledge, the ability to communicate one's knowledge, and the ability to reason using previously learned experiences or procedures.
• Quantitative Reasoning (Gq): the ability to comprehend quantitative concepts and relationships and to manipulate numerical symbols.
• Reading & Writing Ability (Grw): includes basic reading and writing skills.
• Short-Term Memory (Gsm): is the ability to apprehend and hold information in immediate awareness and then use it within a few seconds.
• Long-Term Storage and Retrieval (Glr): is the ability to store information and fluently retrieve it later in the process of thinking.
• Visual Processing (Gv): is the ability to perceive, analyze, synthesize, and think with visual patterns, including the ability to store and recall visual representations.
• Auditory Processing (Ga): is the ability to analyze, synthesize, and discriminate auditory stimuli, including the ability to process and discriminate speech sounds that may be presented under distorted conditions.
• Processing Speed (Gs): is the ability to perform automatic cognitive tasks, particularly when measured under pressure to maintain focused attention.
• Decision/Reaction Time/Speed (Gt): reflect the immediacy with which an individual can react to stimuli or a task (typically measured in seconds or fractions of seconds; not to be confused with Gs, which typically is measured in intervals of 2–3 minutes). See Mental chronometry.

Modern tests do not necessarily measure of all of these broad abilities. For example, Gq and Grw may be seen as measures of school achievement and not IQ.^[7] Gt may be difficult to measure without special equipment.

g was earlier often subdivided into only Gf and Gc which were thought to correspond to the Nonverbal or Performance subtests and Verbal subtests in earlier versions of the popular Wechsler IQ test. More recent research has shown the situation to be more complex.^[7]

Modern comprehensive IQ tests no longer give a single score. Although they still give an overall score, they now also give scores for many of these more restricted abilities, identifying particular strengths and weaknesses of an individual.^[7]

Other theories[link]

J.P. Guilford's Structure of Intellect (1967) model used three dimensions which when combined yielded a total of 120 types of intelligence. It was popular in the 1970s and early 1980s but faded due to both practical problems and theoretical criticisms.^[7]

Alexander Luria's earlier work on neuropsychological processes lead to the PASS theory (1997). It argued that only looking at one general factor was inadequate for researchers and clinicians who worked with learning disabilities, attention disorders, mental retardation, and interventions for such disabilities. The PASS model covers four kinds of processes. The (P)lanning processes involve decision making, problem solving, and performing activities and requires goal setting and self-monitoring. The (A)ttention/arousal process involves selectively attending to a particular stimulus, ignoring distractions, and maintaining vigilance. (S)imultaneous processing involves the integration of stimuli into a group and requires the observation of relationships. (S)uccessive processing involves the integration of stimuli into serial order. The planning and attention/arousal components comes from structures located in the frontal lobe, and the simultaneous and successive processes come from structures located in the posterior region of the cortex.^[18][19][20] It has influenced some recent IQ tests and been seen as a complement to the Cattell-Horn-Carroll theory described above.^[7]

Modern tests[link]

Well-known modern IQ tests include Wechsler Adult Intelligence Scale, Wechsler Intelligence Scale for Children, Stanford-Binet, Woodcock-Johnson Tests of Cognitive Abilities, Kaufman Assessment Battery for Children, and Raven's Progressive Matrices.

Approximately 95% of the population have scores within two standard deviations (SD) of the mean. If one SD is 15 points, as is common in almost all modern tests, then 95% of the population are within a range of 70 to 130, and 98% are below 131. Alternatively, two-thirds of the population have IQ scores within one SD of the mean, i.e. within the range 85-115.

IQ scales are ordinally scaled.^{[21][22][23][24]} While one standard deviation is 15 points, and two SDs are 30 points, and so on, this does not imply that mental ability is linearly related to IQ, such that IQ 50 means half the cognitive ability of IQ 100. In particular, IQ points are not percentage points.

The correlation between IQ test results and achievement test results is about 0.7.^[7][25]

Mental age vs. modern method[link]

The IQs of a large enough population are calculated so that they conform^[26] to a normal distribution with a mean of 100 and a standard deviation of 15.

German psychologist William Stern proposed a method of scoring children's intelligence tests in 1912. He calculated what he called a Intelligenz-Quotient score, or IQ, as the quotient of the mental age (the age group which scored such a result on average) of the test-taker and the chronological age of the test-taker, multiplied by 100. Terman used this system for the first version of the Stanford-Binet Intelligence Scales.^[27] This method has several problems such as the fact that it cannot be used to score adults.

Wechsler introduced a different procedure for his test that is now used by almost all IQ tests. When an IQ test is constructed, a standardization sample representative of the general population takes the test. The median result is defined to be equivalent to 100 IQ points. In almost all modern tests, a standard deviation of the results is defined to be equivalent to 15 IQ points. When a subject takes an IQ test, the result is ranked compared to the results of the standardization sample and the subject is given an IQ score equal to those with the same test result in the standardization sample.

The values of 100 and 15 were chosen in order to get somewhat similar scores as in the older type of test. Likely as a part of the rivalry between the Binet and the Wechsler, the Binet until 2003 chose to have 16 for one SD, causing considerable confusion. Today almost all tests use 15 for one SD. Modern scores are sometimes referred to as "deviation IQs," while older method age-specific scores are referred to as "ratio IQs."^[7][28]

Reliability and validity[link]

Psychometricians generally regard IQ tests as having high statistical reliability. A high reliability implies that while test-takers can have varying scores on differing occasions when taking the same test and can vary in scores on different IQ tests taken at the same age, the scores generally agree. A test-taker's score on any 1 IQ test is surrounded by an error band that shows, to a specified degree of confidence, what the test-taker's true score is likely to be. For modern tests, the standard error of measurement is about 3 points, or in other words, the odds are about 2 out of 3 that a person's true IQ is in range from 3 points above to 3 points below the test IQ. Another description is there is a 95% chance the true IQ is in range from 4-5 points above to 4-5 points below the test IQ, depending on the test in question. Clinical psychologists generally regard them as having sufficient statistical validity for many clinical purposes.^[7][30][31]

Flynn effect[link]

Since the early 20th century, raw scores on IQ tests have increased in most parts of the world.^[32][33][34] When a new version of an IQ test is normed, the standard scoring is set so that performance at the population median results in a score of IQ 100. The phenomenon of rising raw score performance means that if test-takers are scored by a constant standard scoring rule, IQ test scores have been rising at an average rate of around three IQ points per decade. This phenomenon was named the Flynn effect in the book The Bell Curve after James R. Flynn, the author who did the most to bring this phenomenon to the attention of psychologists.^[35][36]

Researchers have been exploring the issue of whether the Flynn effect is equally strong on performance of all kinds of IQ test items, whether the effect may have ended in some developed nations, whether or not there are social subgroup differences in the effect, and what possible causes of the effect might be.^[37] Flynn's observation has prompted much new research in psychology and "demolish some long-cherished beliefs, and raise a number of other interesting issues along the way."^[33]

IQ and age[link]

IQ can change to some degree over the course of childhood.^[38] However, in one longitudinal study, the mean IQ scores of tests at ages 17 and 18 were correlated at r=.86 with the mean scores of tests at ages 5, 6 and 7 and at r=.96 with the mean scores of tests at ages 11, 12 and 13.^[39]

IQ scores for children are relative to children of a similar age. That is, a child of a certain age does not do as well on the tests as an older child or an adult with the same IQ. But relative to persons of a similar age, or other adults in the case of adults, they do equally well if the IQ scores are the same.^[39]

For decades, it has been reported in practitioners' handbooks and textbooks on IQ testing that IQ declines with age after the beginning of adulthood. However, later researchers pointed out that this phenomenon is related to the Flynn effect and is in part a cohort effect rather than a true aging effect.

There have been a variety of studies of IQ and aging since the norming of the first Wechsler Intelligence Scale drew attention to IQ differences in different age groups of adults. Current consensus is that fluid intelligence generally declines with age after early adulthood, while crystallized intelligence remains intact. Both cohort effects (the birth year of the test-takers) and practice effects (test-takers taking the same form of IQ test more than once) must be controlled to gain accurate data. It is unclear whether any lifestyle intervention can preserve fluid intelligence into older ages.^[40]

The peak of capacity for both fluid intelligence and crystallized intelligence occurs at age 26. This is followed by a slow decline.^[41]

Genetics and environment[link]

Environmental and genetic factors play a role in determining IQ. Their relative importance have been the subject of much research and debate.

Heritability[link]

Heritability is defined as the proportion of variance in a trait which is attributable to genotype within a defined population in a specific environment. There are a number of points to consider when interpreting heritability.^[42] Heritability measures the proportion of variation in a trait can be attributed to genes, and not the proportion of a trait caused by genes. The value of heritability can change if the impact of environment (or of genes) in the population is substantially altered. A high heritability of a trait does not mean that environmental effects such as learning are not involved. Since heritability increases during childhood and adolescence, one should be cautious drawing conclusions regarding the role of genetics and environment from studies where the participants are not followed until they are adults.

Studies have found the heritability of IQ in adult twins to be 0.7 to 0.8 and in children twins 0.45 in the Western world.^[39][43][44] It may seem reasonable to expect that genetic influences on traits like IQ should become less important as one gains experiences with age. However, the opposite occurs. Heritability measures in infancy are as low as 0.2, around 0.4 in middle childhood, and as high as 0.8 in adulthood.^[45] One proposed explanation is that people with different genes tend to reinforce the effects of those genes, for example by seeking out different environments.^[39] There is an ongoing debate about whether these heritability estimates are too high due to not adequately considering various factors, such as that the environment may be relatively more important in families with low socio-economic status or the effect of the maternal (fetal) environment.

Shared family environment[link]

There are aspects of environments that family members have in common (for example, characteristics of the home). This shared family environment accounts for 0.25–0.35 of the variation in IQ in childhood. By late adolescence it is quite low (zero in some studies). There is a similar effect for several other psychological traits. These studies have not looked at the effects of extreme environments such as in abusive families.^{[39][46][47][48]}

Non-shared family environment and environment outside the family[link]

Although parents treat their children differently, such differential treatment explains only a small amount of non-shared environmental influence. One suggestion is that children react differently to the same environment due to different genes. More likely influences may be the impact of peers and other experiences outside the family.^[39][47]

Individual genes[link]

A number of individual genes have been reported to be associated with IQ. Examples include CHRM2, microcephalin, and ASPM. However, Deary and colleagues (2009) argued that there are still almost no replicated evidence.^[49] About 20,000 genes are thought to have an impact on the development and functionality of the brain.^[50]

Gene-environment interaction[link]

Dickens and Flynn (2001) argued the "heritability" figure includes both a direct effect of the genotype on IQ and also indirect effects where the genotype changes the environment, in turn affecting IQ. That is, those with a higher IQ tend to seek out stimulating environments that further increase IQ. The direct effect can initially have been very small but feedback loops can create large differences in IQ. In their model, an environmental stimulus can have a very large effect on IQ, even in adults, but this effect also decays over time unless the stimulus continues (the model could be adapted to include possible factors, like nutrition in early childhood, that may cause permanent effects). The Flynn effect can be explained by a generally more stimulating environment for all people. The authors suggest that programs aiming to increase IQ would be most likely to produce long-term IQ gains if they taught children how to replicate outside the program the kinds of cognitively demanding experiences that produce IQ gains while they are in the program and motivate them to persist in that replication long after they have left the program.^[51][52]

Interventions[link]

In general, educational interventions, as those described below, have shown short-term effects on IQ, but long-term follow-up is often missing. For example, in the US some interventive programs such as the Head Start Program have not produced lasting gains in IQ scores, although the more intensive Abecedarian Project have.^[39]

A placebo controlled double-blind experiment found that vegetarians who took 5 grams of creatine per day for six weeks showed a significant improvement on two separate tests of fluid intelligence, Raven's Progressive Matrices, and the backward digit span test from the WAIS. The treatment group was able to repeat longer sequences of numbers from memory and had higher overall IQ scores than the control group. The researchers concluded that "supplementation with creatine significantly increased intelligence compared with placebo."^[53] A subsequent study found that creatine supplements improved cognitive ability in the elderly.^[54] However, a study on young adults (0.03 g/kg/day for six weeks, e.g., 2 g/day for 150-pound individual) failed, to find any improvements.^[55]

Recent studies have shown that training in using one's working memory may increase IQ. A study on young adults published in April 2008 by a team from the Universities of Michigan and Bern supports the possibility of the transfer of fluid intelligence from specifically designed working memory training.^[56][57] Further research will be needed to determine nature, extent and duration of the proposed transfer. Among other questions, it remains to be seen whether the results extend to other kinds of fluid intelligence tests than the matrix test used in the study, and if so, whether, after training, fluid intelligence measures retain their correlation with educational and occupational achievement or if the value of fluid intelligence for predicting performance on other tasks changes. It is also unclear whether the training is durable of extended periods of time.^[58]

Music and IQ[link]

Musical training in childhood been found to correlate with higher than average IQ.^[59] In a 2004 study conducted by E. Glenn Schellenberg, results showed that 6 year old children who received musical training (voice or piano lessons) had an average increase in IQ of 7.0 points while children who received alternative training (i.e. drama) or no training had an average increase in IQ of only 4.3 points (which may be consequence of the children entering grade school) as indicated by full scale IQ. Children were tested using Wechsler Intelligence Scale for Children–Third Edition, Kaufman Test of Educational Achievement and Parent Rating Scale of the Behavioral Assessment System for Children. ^[59]

Listening to classical music has also been found to increase IQ; specifically spatial ability. In 1994 Frances Rauscher and Gorden Shaw found that when college students listened to 10 minutes of Mozart's Sonata for Two Pianos, there is an IQ increase of 8 to 9 points on the spatial subtest on the Standford-Binet Intelligence Scale.^[60] However, this effect is a short term effect and usually lasts no longer than 10 to 15 minutes. This term was coined the Mozart effect.

IQ and brain anatomy[link]

Several neurophysiological factors have been correlated with intelligence in humans, including the ratio of brain weight to body weight and the size, shape and activity level of different parts of the brain. Specific features that may affect IQ include the size and shape of the frontal lobes, the amount of blood and chemical activity in the frontal lobes, the total amount of gray matter in the brain, the overall thickness of the cortex and the glucose metabolic rate.

Health and IQ[link]

Health is important in understanding differences in IQ test scores and other measures of cognitive ability. Several factors can lead to significant cognitive impairment, particularly if they occur during pregnancy and childhood when the brain is growing and the blood–brain barrier is less effective. Such impairment may sometimes be permanent, sometimes be partially or wholly compensated for by later growth.^{[citation needed]}

Developed nations have implemented several health policies regarding nutrients and toxins known to influence cognitive function. These include laws requiring fortification of certain food products and laws establishing safe levels of pollutants (e.g. lead, mercury, and organochlorides). Improvements in nutrition, and in public policy in general, have been implicated in worldwide IQ increases.^{[citation needed]}

Cognitive epidemiology is a field of research that examines the associations between intelligence test scores and health. Researchers in the field argue that intelligence measured at an early age is an important predictor of later health and mortality differences.

Social outcomes[link]

Outside of academic research and medicine, IQ testing is often done due to its ability to predict future job performance, social pathologies, or academic achievement. Academic research has also examined these associations, as well as the effect of IQ on other social outcomes, such as income and wealth.

Many of the arguments and criticisms assume that explained variance can be calculated as the square of the correlation coefficient. This way of calculating explained variance has been criticized as inappropriate for most social scientific work.^[61] Also, as for the heritability figure, the explained variance only refers to the proportion of variation in an outcome that is explained by a factor, and not the proportion of an outcome that is explained by a factor.

Other tests[link]

One study found a correlation of 0.82 between g (general intelligence factor) and SAT scores;^[62] another has found correlation of 0.81 between g and GCSE scores.^[63]

Correlations between IQ scores (general cognitive ability) and achievement test scores are reported to be 0.81 by Deary and colleagues, with the explained variance ranging "from 58.6% in Mathematics and 48% in English to 18.1% in Art and Design".^[63]

School performance[link]

The American Psychological Association's report "Intelligence: Knowns and Unknowns" states that wherever it has been studied, children with high scores on tests of intelligence tend to learn more of what is taught in school than their lower-scoring peers. The correlation between IQ scores and grades is about .50. This means that the explained variance is 25%. Achieving good grades depends on many factors other than IQ, such as "persistence, interest in school, and willingness to study" (p. 81).^[39]

It has been found IQ correlation with school performance depends on the IQ measurement used. For undergraduate students, the Verbal IQ as measured by WAIS-R has been found to correlate significantly (0.53) with the GPA of the last 60 hours. In contrast, Performance IQ correlation with the same GPA was only 0.22 in the same study.^[64]

Job performance[link]

According to Frank Schmidt and John Hunter, "for hiring employees without previous experience in the job the most valid predictor of future performance is general mental ability."^[65] The validity of IQ as a predictor of job performance is above zero for all work studied to date, but varies with the type of job and across different studies, ranging from 0.2 to 0.6.^[66] The correlations were higher when the unreliability of measurement methods were controlled for.^[39] While IQ is more strongly correlated with reasoning and less so with motor function,^[67] IQ-test scores predict performance ratings in all occupations.^[65] That said, for highly qualified activities (research, management) low IQ scores are more likely to be a barrier to adequate performance, whereas for minimally-skilled activities, athletic strength (manual strength, speed, stamina, and coordination) are more likely to influence performance.^[65] It is largely mediated through the quicker acquisition of job-relevant knowledge that IQ predicts job performance.

In establishing a causal direction to the link between IQ and work performance, longitudinal studies by Watkins and others suggest that IQ exerts a causal influence on future academic achievement, whereas academic achievement does not substantially influence future IQ scores.^[68] Treena Eileen Rohde and Lee Anne Thompson write that general cognitive ability but not specific ability scores predict academic achievement, with the exception that processing speed and spatial ability predict performance on the SAT math beyond the effect of general cognitive ability.^[69]

The US military has minimum enlistment standards at about the IQ 85 level. There have been two experiments with lowering this to 80 but in both cases these men could not master soldiering well enough to justify their costs ^[70]

Some US police departments have set a maximum IQ score for new officers (for example: 125, in New London, CT), under the argument that those with overly-high IQs will become bored and exhibit high turnover in the job. This policy has been challenged as discriminatory, but upheld by at least one US District court. ^[71]

The American Psychological Association's report "Intelligence: Knowns and Unknowns" states that since the explained variance is 29%, other individual characteristics such as interpersonal skills, aspects of personality etc. are probably of equal or greater importance, but at this point there are no equally reliable instruments to measure them.^[39]

Income[link]

Some researchers claim "in economic terms it appears that the IQ score measures something with decreasing marginal value. It is important to have enough of it, but having lots and lots does not buy you that much."^[72][73]

Other studies show that ability and performance for jobs are linearly related, such that at all IQ levels, an increase in IQ translates into a concomitant increase in performance.^[74] Charles Murray, coauthor of The Bell Curve, found that IQ has a substantial effect on income independently of family background.^[75]

Taking the above two principles together, very high IQ produces very high job performance, but no greater income than slightly high IQ. Studies also show that high IQ is related to higher net worth.^[76]

The American Psychological Association's 1995 report Intelligence: Knowns and Unknowns stated that IQ scores accounted for (explained variance) about quarter of the social status variance and one-sixth of the income variance. Statistical controls for parental SES eliminate about a quarter of this predictive power. Psychometric intelligence appears as only one of a great many factors that influence social outcomes.^[39]

Some studies claim that IQ only accounts for (explained variance) a sixth of the variation in income because many studies are based on young adults (many of whom have not yet completed their education). On pg 568 of The g Factor, Arthur Jensen claims that although the correlation between IQ and income averages a moderate 0.4 (one sixth or 16% of the variance), the relationship increases with age, and peaks at middle age when people have reached their maximum career potential. In the book, A Question of Intelligence, Daniel Seligman cites an IQ income correlation of 0.5 (25% of the variance).

A 2002 study^[77] further examined the impact of non-IQ factors on income and concluded that an individual's location, inherited wealth, race, and schooling are more important as factors in determining income than IQ.

IQ and crime[link]

The American Psychological Association's 1995 report Intelligence: Knowns and Unknowns stated that the correlation between IQ and crime was -0.2. It was -0.19 between IQ scores and number of juvenile offenses in a large Danish sample; with social class controlled, the correlation dropped to -0.17. A correlation of 0.20 means that the explained variance is less than 4%. It is important to realize that the causal links between psychometric ability and social outcomes may be indirect. Children with poor scholastic performance may feel alienated. Consequently, they may be more likely to engage in delinquent behavior, compared to other children who do well.^[39]

In his book The g Factor (1998), Arthur Jensen cited data which showed that, regardless of race, people with IQs between 70 and 90 have higher crime rates than people with IQs below or above this range, with the peak range being between 80 and 90.

The 2009 Handbook of Crime Correlates stated that reviews have found that around eight IQ points, or 0.5 SD, separate criminals from the general population, especially for persistent serious offenders. It has been suggested that this simply reflects that "only dumb ones get caught" but there is similarly a negative relation between IQ and self-reported offending. That children with conduct disorder have lower IQ than their peers "strongly argues" for the theory.^[78]

A study of the relationship between US county-level IQ and US county-level crime rates found that higher average IQs were associated with lower levels of property crime, burglary, larceny rate, motor vehicle theft, violent crime, robbery, and aggravated assault. These results were not "confounded by a measure of concentrated disadvantage that captures the effects of race, poverty, and other social disadvantages of the county."^[79]

Other correlations with IQ[link]

In addition, IQ and its correlation to health, violent crime, gross state product, and government effectiveness are the subject of a 2006 paper in the publication Intelligence. The paper breaks down IQ averages by U.S. states using the federal government's National Assessment of Educational Progress math and reading test scores as a source.^[80]

The American Psychological Association's 1995 report Intelligence: Knowns and Unknowns stated that the correlations for most "negative outcome" variables are typically smaller than 0.20, which means that the explained variance is less than 4%.^[39]

Tambs et al.^{[81][better source needed]} found that occupational status, educational attainment, and IQ are individually heritable; and further found that "genetic variance influencing educational attainment ... contributed approximately one-fourth of the genetic variance for occupational status and nearly half the genetic variance for IQ." In a sample of U.S. siblings, Rowe et al.^[82] report that the inequality in education and income was predominantly due to genes, with shared environmental factors playing a subordinate role.

A recent USA study connecting political views and intelligence has shown that the mean adolescent intelligence of young adults who identify themselves as "very liberal" is 106.4, while that of those who identify themselves as "very conservative" is 94.8.^[83] Two other studies conducted in the UK reached similar conclusions.^[84][85]

There are also other correlations such as those between religiosity and intelligence and fertility and intelligence.

Real-life accomplishments[link]

Average adult combined IQs associated with real-life accomplishments by various tests:^[86][87]

• MDs, JDs, or PhDs 125+ (WAIS-R, 1987)
• College graduates 112 (KAIT, 2000; K-BIT, 1992), 115 (WAIS-R)
• 1–3 years of college 104 (KAIT, K-BIT), 105-110 (WAIS-R)
• Clerical and sales workers 100-105
• High school graduates, skilled workers (e.g., electricians, cabinetmakers) 100 (KAIT, WAIS-R), 97 (K-BIT)
• 1–3 years of high school (completed 9–11 years of school) 94 (KAIT), 90 (K-BIT), 95 (WAIS-R)
• Semi-skilled workers (e.g., truck drivers, factory workers) 90-95
• Elementary school graduates (completed eighth grade) 90
• Elementary school dropouts (completed 0–7 years of school) 80-85
• Have 50/50 chance of reaching high school 75

Average IQ of various occupational groups:^[88]

• Professional and technical 112
• Police Officers 104
• Managers and administrators 104
• Clerical workers; sales workers; skilled workers, craftsmen, and foremen 101
• Semi-skilled workers (operatives, service workers, including private household) 92
• Unskilled workers 87

Type of work that can be accomplished:^[86]

• Adults can harvest vegetables, repair furniture 60
• Adults can do domestic work 50
• Adults can mow lawns, do simple laundry 40

There is considerable variation within and overlap between these categories. People with high IQs are found at all levels of education and occupational categories. The biggest difference occurs for low IQs with only an occasional college graduate or professional scoring below 90.^[7]

Group differences[link]

Among the most controversial issues related to the study of intelligence is the observation that intelligence measures such as IQ scores vary between ethnic and racial groups and sexes. While there is little scholarly debate about the existence of some of these differences, their causes remain highly controversial both within academia and in the public sphere.

Sex[link]

Most IQ tests are constructed so that there are no overall score differences between females and males. Because environmental factors affect brain activity and behavior, where differences are found, it can be difficult for researchers to assess whether or not the differences are innate. Areas where differences have been found include verbal and mathematical ability.

Race[link]

The 1996 Task Force investigation on Intelligence sponsored by the American Psychological Association concluded that there are significant variations in IQ across races.^[39] The problem of determining the causes underlying this variation relates to the question of the contributions of "nature and nurture" to IQ. Psychologists such as Alan S. Kaufman^[89] and Nathan Brody^[90] and statisticians such as Bernie Devlin^[91] argue that there are insufficient data to conclude that this is because of genetic influences. One of the most notable researchers arguing for a strong genetic influence on these average score differences is Arthur Jensen. In contrast, other researchers such as Richard Nisbett argue that environmental factors can explain all of the average group differences.^[92]

Public policy[link]

The examples and perspective in this article deal primarily with the United States and do not represent a worldwide view of the subject. Please improve this article and discuss the issue on the talk page. (August 2010)

In the United States, certain public policies and laws regarding military service,^{[93] [94]} education, public benefits,^[95] capital punishment,^[96] and employment incorporate an individual's IQ into their decisions. However, in the case of Griggs v. Duke Power Co. in 1971, for the purpose of minimizing employment practices that disparately impacted racial minorities, the U.S. Supreme Court banned the use of IQ tests in employment, except when linked to job performance via a Job analysis. Internationally, certain public policies, such as improving nutrition and prohibiting neurotoxins, have as one of their goals raising, or preventing a decline in, intelligence.

A diagnosis of mental retardation is in part based on the results of IQ testing. Borderline intellectual functioning is a categorization where a person has below average cognitive ability (an IQ of 71–85), but the deficit is not as severe as mental retardation (70 or below).

In the United Kingdom, the eleven plus exam which incorporated an intelligence test has been used from 1945 to decide, at eleven years old, which type of school a child should go to. They have been much less used since the widespread introduction of comprehensive schools.

Criticism and views[link]

Relation between IQ and intelligence[link]

IQ is the most researched approach to intelligence and by far the most widely used in practical setting. However, although IQ attempts to measure some notion of intelligence, it may fail to act as an accurate measure of "intelligence" in its broadest sense. IQ tests only examine particular areas embodied by the broadest notion of "intelligence", failing to account for certain areas which are also associated with "intelligence" such as creativity or emotional intelligence.

There are critics such as Keith Stanovich who do not dispute the stability of IQ test scores or the fact that they predict certain forms of achievement rather effectively. They do argue, however, that to base a concept of intelligence on IQ test scores alone is to ignore many important aspects of mental ability.^[3][97]

[edit] Criticism of g

Some scientists dispute IQ entirely. In The Mismeasure of Man (1996), paleontologist Stephen Jay Gould criticized IQ tests and argued that that they were used for scientific racism. He argued that g was a mathematical artifact and criticized:

...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)

Psychologist Peter Schönemann was also a persistent critic of IQ, calling it "the IQ myth". He argued that g is a flawed theory and that the high heritability estimates of IQ are based on false assumptions.^[98][99]

Psychologist Arthur Jensen has rejected the criticism by Gould and also argued that even if g was replaced by a model with several intelligences this would change the situation less than expected. All tests of cognitive ability would continue to be highly correlated with one another and there would still be a black-white gap on cognitive tests.^[100]

Test bias[link]

The American Psychological Association's report Intelligence: Knowns and Unknowns stated that in the United States IQ tests as predictors of social achievement are not biased against African Americans since they predict future performance, such as school achievement, similarly to the way they predict future performance for Caucasians.^[39]

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,"^[101] 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.^[102][103] Standard intelligence tests, such as the Stanford-Binet, are often inappropriate for children with autism; the alternative of using developmental or adaptive skills measures are relatively poor measures of intelligence in autistic children, and may have resulted in incorrect claims that a majority of children with autism are mentally retarded.^[104]

Outdated methodology[link]

A 2006 article stated that contemporary psychologic research often did not reflect substantial recent developments in psychometrics and "bears an uncanny resemblance to the psychometric state of the art as it existed in the 1950s." ^[105]

"Intelligence: Knowns and Unknowns"[link]

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 report on the state of intelligence research which could be used by all sides as a basis for discussion, "Intelligence: Knowns and Unknowns". The full text of the report is available through several websites.^[39][106]

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 stated that individual differences in intelligence are substantially influenced by both genetics and environment.

The report stated that a number of biological factors, including malnutrition, exposure to toxic substances, and various prenatal and perinatal stressors, result in lowered psychometric intelligence under at least some conditions. The task force agrees that large differences do exist between the average IQ scores of blacks and whites, saying:

The cause of that differential is not known; it is apparently not due to any simple form of bias in the content or administration of the tests themselves. The Flynn effect shows that environmental factors can produce differences of at least this magnitude, but that effect is mysterious in its own right. Several culturally based explanations of the Black/ White IQ differential have been proposed; some are plausible, but so far none has been conclusively supported. There is even less empirical support for a genetic interpretation. In short, no adequate explanation of the differential between the IQ means of Blacks and Whites is presently available.

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.

High IQ societies[link]

There are social organizations, some international, which limit membership to people who have scores as high as or higher than the 98th percentile on some IQ test or equivalent. Mensa International is perhaps the most well known of these. There are other groups requiring a score above the 98th percentile.

Reference charts[link]

IQ reference charts are tables suggested by test publishers to divide intelligence ranges in various categories.

See also[link]

References[link]

Further reading[link]

External links[link]

• Human Intelligence: biographical profiles, current controversies, resources for teachers
• Classics in the History of Psychology

William Bradford Shockley Jr.
Born	(1910-02-13)February 13, 1910 London, England, United Kingdom
Died	August 12, 1989(1989-08-12) (aged 79) Stanford, California, United States
Nationality	American
Institutions	Bell Labs Shockley Semiconductor Stanford University
Alma mater	Caltech MIT
Doctoral advisor	John C. Slater
Known for	Transistor
Notable awards	Nobel Prize in Physics (1956) Comstock Prize in Physics (1953) IEEE Medal of Honor(1980)

William Bradford Shockley Jr. (February 13, 1910 – August 12, 1989) was an American physicist and inventor. Along with John Bardeen and Walter Houser Brattain, Shockley co-invented the transistor, for which all three were awarded the 1956 Nobel Prize in Physics.

Shockley's attempts to commercialize a new transistor design in the 1950s and 1960s led to California's "Silicon Valley" becoming a hotbed of electronics innovation. In his later life, Shockley was a professor at Stanford and became a staunch advocate of eugenics.^[1]

Biography[link]

Early years[link]

Shockley was born in London, England to American parents, and raised in his family's hometown of Palo Alto, California, from age three.^[2] His father, William senior, was a mining engineer who speculated in mines for a living, and spoke eight languages. His mother, Mary, grew up in the American West, graduated from Stanford University, and became the first female US Deputy mining surveyor.^[3]

He received his Bachelor of Science degree from the California Institute of Technology in 1932. While still a student, Shockley married Iowan Jean Bailey in August 1933. In March 1934 Jean had a baby girl, Alison; she also had a son, Richard (Dick) who also became a physicist. Shockley was awarded his PhD from the Massachusetts Institute of Technology in 1936. The title of his doctoral thesis was Electronic Bands in Sodium Chloride, and was suggested by his thesis advisor, John C. Slater. After receiving his doctorate, he joined a research group headed by Clinton Davisson at Bell Labs in New Jersey. The next few years were productive ones for Shockley. He published a number of fundamental papers on solid state physics in Physical Review. In 1938, he got his first patent, "Electron Discharge Device" on electron multipliers.

When World War II broke out, Shockley became involved in radar research at the labs in Whippany, New Jersey. In May 1942 he took leave from Bell Labs to become a research director at Columbia University's Anti-Submarine Warfare Operations Group.^[4] This involved devising methods for countering the tactics of submarines with improved convoying techniques, optimizing depth charge patterns, and so on. This project required frequent trips to the Pentagon and Washington, where Shockley met many high ranking officers and government officials. In 1944 he organized a training program for B-29 bomber pilots to use new radar Bombsights. In late 1944 he took a three month tour to bases around the world to assess the results. For this project, Secretary of War Robert Patterson awarded Shockley the Medal for Merit on October 17, 1946.

In July 1945, the War Department asked Shockley to prepare a report on the question of probable casualties from an invasion of the Japanese mainland. Shockley concluded:

If the study shows that the behavior of nations in all historical cases comparable to Japan's has in fact been invariably consistent with the behavior of the troops in battle, then it means that the Japanese dead and ineffectives at the time of the defeat will exceed the corresponding number for the Germans. In other words, we shall probably have to kill at least 5 to 10 million Japanese. This might cost us between 1.7 and 4 million casualties including 400,000 to 800,000 killed.^[5]

This prediction influenced the decision for the atomic bombings of Hiroshima and Nagasaki to force Japan to surrender without an invasion.^[6]

Solid-state transistor[link]

Shortly after the end of the war in 1945, Bell Labs formed a Solid State Physics Group, led by Shockley and chemist Stanley Morgan, which included John Bardeen, Walter Brattain, physicist Gerald Pearson, chemist Robert Gibney, electronics expert Hilbert Moore, and several technicians. Their assignment was to seek a solid-state alternative to fragile glass vacuum tube amplifiers. Its first attempts were based on Shockley's ideas about using an external electrical field on a semiconductor to affect its conductivity. These experiments failed every time in all sorts of configurations and materials. The group was at a standstill until Bardeen suggested a theory that invoked surface states that prevented the field from penetrating the semiconductor. The group changed its focus to study these surface states and they met almost daily to discuss the work. The rapport of the group was excellent, and ideas were freely exchanged.^[7]

By the winter of 1946 they had enough results that Bardeen submitted a paper on the surface states to Physical Review. Brattain started experiments to study the surface states through observations made while shining a bright light on the semiconductor's surface. This led to several more papers (one of them co-authored with Shockley), which estimated the density of the surface states to be more than enough to account for their failed experiments. The pace of the work picked up significantly when they started to surround point contacts between the semiconductor and the conducting wires with electrolytes. Moore built a circuit that allowed them to vary the frequency of the input signal easily. Finally they began to get some evidence of power amplification when Pearson, acting on a suggestion by Shockley, put a voltage on a droplet of glycol borate (a viscous chemical that did not evaporate) placed across a P-N junction.^[8]

John Bardeen, William Shockley and Walter Brattain at Bell Labs, 1948.

December 1947 was Bell Labs' "Miracle Month," when Bardeen and Brattain – working without Shockley – succeeded in creating a point-contact transistor that achieved amplification. Within the next month, Bell Labs' patent attorneys started to work on the patent applications.

Bell Labs' attorneys soon discovered Shockley's field effect principle had been anticipated and devices based on it patented in 1930 by Julius Lilienfeld, who filed his MESFET-like patent in Canada on October 22, 1925.^[9][10] Although the patent appeared "breakable" (it could not work) the patent attorneys based one of its four patent applications only on the Bardeen-Brattain point contact design. Three others (submitted first) covered the electrolyte-based transistors with Bardeen, Gibney and Brattain as the inventors. Shockley's name was not on any of these patent applications. This angered Shockley, who thought his name should also be on the patents because the work was based on his field effect idea. He even made efforts to have the patent written only in his name, and told Bardeen and Brattain of his intentions.^[11]

At the same time he secretly continued his own work to build a different sort of transistor based on junctions instead of point contacts; he expected this kind of design would be more likely to be commercially viable. The point contact transistor, he believed, would prove to be fragile and difficult to manufacture. Shockley was also dissatisfied with certain parts of the explanation for how the point contact transistor worked and conceived of the possibility of minority carrier injection. On February 13, 1948 another team member, John N. Shive, built a point contact transistor with bronze contacts on the front and back of thin wedge of germanium, proving that holes could diffuse through bulk germanium and not just along the surface as previously thought.^{[12]:153[13]:145} Shive's invention sparked^[14] Shockley's invention of the junction transistor.^[12]:143 Shockley later admitted that the workings of the team were "mixture of cooperation and competition." He also admitted that he kept some of own work secret until his "hand was forced" by Shive's 1948 advance.^[15] Shockley worked out a rather complete description of what he called the "sandwich" transistor, and a first proof of principle was obtained on April 7, 1949.

This resulted in his invention of the junction transistor, which was announced at a press conference on July 4, 1951. Shockley obtained a patent for this invention on September 25, 1951. Different fabrication methods for this device were developed over the next several years, but a diffusion based/photolithographic procedure quickly became the method of choice for many applications. It soon eclipsed the point contact transistor, and it and its offspring became overwhelmingly dominant in the marketplace for many years. Shockley continued as a group head to lead much of the effort at Bell Labs to improve it and its fabrication for two more years.

Meanwhile, Shockley worked furiously on his magnum opus, Electrons and Holes in Semiconductors which was finally published as a 558 page treatise in 1950. In it, Shockley worked out the critical ideas of drift and diffusion and the differential equations that govern the flow of electrons in solid state crystals. Shockley's diode equation is also described. This seminal work became the "bible" for an entire generation of scientists working to develop and improve new variants of the transistor and other devices based on semiconductors.

In 1951, he was elected a member of the National Academy of Sciences (NAS). He was forty-one years old; this was rather young for such an election. Two years later, he was chosen as the recipient of the prestigious Comstock Prize^[16] for Physics by the NAS, and was the recipient of many other awards and honors.

The ensuing publicity generated by the "invention of the transistor" often thrust Shockley to the fore, much to the chagrin of Bardeen and Brattain. Bell Labs management, however, consistently presented all three inventors as a team. Though Shockley would correct the record where reporters gave him sole credit for the invention,^[17] he eventually infuriated and alienated Bardeen and Brattain, and he essentially blocked the two from working on the junction transistor. Bardeen began pursuing a theory for superconductivity and left Bell Labs in 1951. Brattain refused to work with Shockley further and was assigned to another group. Neither Bardeen nor Brattain had much to do with the development of the transistor beyond the first year after its invention.^[18]

Shockley's abrasive management style caused him to be passed over for executive promotion at Bell Labs, which also felt he was a greater asset as a research scientist and theorist. Shockley wanted the power and profit he felt he deserved. He took a leave from Bell Labs in 1953 and moved back to the California Institute of Technology (Caltech) for four months as a visiting professor.

Shockley Semiconductor[link]

Eventually he was given a chance to run his own company, as a division of a Caltech friend's successful electronics firm. In 1955, Shockley joined Beckman Instruments, where he was appointed as the Director of Beckman's newly founded Shockley Semiconductor Laboratory division at 391 San Antonio Road, Mountain View, California. With his prestige and Beckman's capital, Shockley attempted to lure some of his former colleagues from Bell Labs to his new lab, but none of them would join him. Instead, Shockley started scouring universities for the brightest graduates to build a company from scratch, one that would be run "his way".

"His way" could generally be summed up as domineering and increasingly paranoid. In one well-known incident, he claimed that a secretary's cut thumb was the result of a malicious act and he demanded lie detector tests to find the culprit.^[19] It was later demonstrated the cut was caused by a broken thumbtack on the office door, and the research staff was henceforth increasingly hostile. Meanwhile, his demands to create a new and technically difficult device (originally called a Shockley diode and now modified to become the thyristor), meant that the project was moving very slowly.

In late 1957, eight of Shockley's researchers, who called themselves the "traitorous eight," resigned after Shockley decided not to continue research into silicon-based semiconductors. ^[20] After a meeting with Sherman Fairchild and procurement of seed capital from Fairchild Camera and Instrument Corporation, they started Fairchild Semiconductor. The "traitorous eight" included Robert Noyce and Gordon E. Moore, who would later leave Fairchild and form Intel Corporation. Other offspring companies of Fairchild Semiconductor include National Semiconductor and Advanced Micro Devices.

Thus, over the course of just 20 years, a mere eight of Shockley’s former employees gave forth 65 new enterprises, which then went on to do the same....^[21] Shockley Semiconductor and these companies formed the nucleus of what became Silicon Valley, which revolutionized the world of electronics and, indeed, the world itself.

While Shockley was still trying to get his three-state device to work, Fairchild and Texas Instruments both introduced the first integrated circuits, making Shockley's work in that area essentially superfluous. Shockley did manage to get the three-state device to work but failed to make it commercially successful.

In 1961 he and Hans Queisser derived the maximal theoretical efficiency of a simple solar cell, subsequently known as the Shockley–Queisser limit.

The firm was sold in 1960 and became a part of ITT in 1968.

Sidelights[link]

Shockley was popular as speaker, lecturer, and an amateur magician. He once magically produced a bouquet of roses at the end of his address before the American Physical Society. He was also famed in his early years for his elaborate practical jokes.^[22] He became an accomplished rock climber, going often to the Shawangunks in the Hudson River Valley, where he pioneered a route across an overhang, known to this day as "Shockley's Ceiling."^[8]

He was first to propose a lognormal distribution to model the creation process for scientific research papers.^[23]

He was an atheist.^[24]

Later years[link]

Shockley separated from his wife Jean in the spring of 1954, divorcing her that summer. Shortly after forming Shockley Semiconductor, on November 23, 1955, Shockley married Emmy Lanning, a teacher of psychiatric nursing from upstate New York. They had a very happy marriage that lasted until his death in 1989.

In July 1961, Shockley, his wife, and son Dick were involved in a serious automobile accident: Shockley required several months to recover from his injuries.

When Shockley was eased out of the directorship of Shockley Semiconductor, he joined Stanford University, where he was appointed the Alexander M. Poniatoff Professor of Engineering and Applied Science.^[25]

Shockley's last patent was granted in 1968, for a rather complex semiconductor device.

Statements about populations and genetics[link]

Late in his life, Shockley became intensely interested in questions of race, intelligence, and eugenics. He thought this work was important to the genetic future of the human species, and came to describe it as the most important work of his career, even though expressing such politically unpopular views risked damaging his reputation. When asked why he seemed to take positions associated with both the political right and left, Shockley explained that his goal was "the application of scientific ingenuity to the solution of human problems."^[26]

Shockley argued that the higher rate of reproduction among the less intelligent was having a dysgenic effect, and that a drop in average intelligence would ultimately lead to a decline in civilization.^[27] Shockley advocated that the scientific community should seriously investigate questions of heredity, intelligence, and demographic trends, and suggest policy changes if he was proven right.^[28]

Although Shockley was concerned about dysgenic effects among both blacks and whites, he perceived the situation among blacks as more problematic. According to 1970 US Census, unskilled and skilled whites had on average 3.7 and 2.3 children, respectively, whereas the corresponding numbers for blacks were 5.4 and 1.9.^[29] Shockley expressed concern that the black population would become progressively less intelligent, countering all the gains that had been made by the Civil Rights movement. Shockley's views on this topic, expressed in his publications and lectures, were based in part on the work of Cyril Burt who was discredited by the scientific community in the 1970s, known as the Burt Affair, but was later vindicated by the works of Arthur Jensen and J. Philippe Rushton in 1997 when they too showed very similar results as Burt. Shockley also proposed that individuals with IQs below 100 be paid to undergo voluntary sterilization.

He donated sperm to the Repository for Germinal Choice, a sperm bank founded by Robert Klark Graham in hopes of spreading humanity's best genes. The bank, called by the media the "Nobel Prize sperm bank," claimed to have three Nobel Prize-winning donors, though Shockley was the only one to publicly acknowledge his donation to the sperm bank. However, Shockley's controversial views brought the Repository for Germinal Choice notable publicity and may have discouraged other Nobel Prize winners from donating sperm.^[30]

While the "Nobel sperm bank" issue was in the news, Playboy magazine published in its August 1980 issue a lengthy interview with Shockley. Although Hugh Hefner, the magazine's publisher, was not particularly sympathetic to Shockley's views, this in-depth interview nonetheless provided an opportunity for the professor to clarify his views on eugenics and the social implications of racial differences, and to defend his side of the controversy to a wider audience. In 1981 he filed a libel suit against the Atlanta Constitution after a reporter called him a "Hitlerite" and compared his racial views to those of the Nazis. Shockley won the suit but received only US$1 in damages.^[31][32] Shockley's biographer sums this up as saying that the statement was defamatory, but Shockley's reputation was not worth much by the time the trial reached a verdict.^[33]

In his later years Shockley took several precautions to improve his interactions with the media, to little avail. He taped his telephone conversations with reporters, and then sent the transcript to them by registered mail. At one point he toyed with the idea of making them take a simple quiz on his work before discussing the subject with them. His habit of saving all his papers, even laundry lists, provides abundant documentation for researchers on his life.^[34]

Edgar G. Epps argued that "William Shockley's position lends itself to racist interpretations".^[35] Daniel J. Kevles mentioned that Shockley "invited ridicule as a racist and biological ignoramus".^[36][37] Anthropologist and eugenics advocate Roger Pearson^[38] has defended Shockley, arguing that Shockley’s views were misrepresented in the popular media by journalists who lacked a proper understanding of the topics Shockley wrote about, and that his views were in fact shared by many other scholars who were reluctant to publicly defend him due to fear of being attacked themselves.^[39]

Death[link]

He died in 1989 of prostate cancer.^[1]

By the time of his death he was almost completely estranged from most of his friends and family, except his wife. His children are reported to have learned of his death only through the print media.^[40]

A group of about 30 colleagues, who have met on and off since 1956, met at Stanford in 2002 to reminisce about their time with Shockley and his central role in sparking the information technology revolution, its organizer saying "Shockley is the man who brought silicon to Silicon Valley."^[41]

Honors[link]

• He received the Comstock Prize in Physics of the National Academy of Sciences in 1953.^[42]
• He was the first recipient of the Oliver E. Buckley Solid State Physics Prize of the American Physical Society in 1953.
• Shockley was a co-recipient of the Nobel Prize in physics in 1956, along with Bardeen and Brattain. In his Nobel lecture, he gave full credit to Brattain and Bardeen as the inventors of the point-contact transistor. The three of them, together with wives and guests, had a rather raucous late-night champagne-fueled party to celebrate together.
• Holley Medal of the American Society of Mechanical Engineers in 1963.
• He received honorary science doctorates from the University of Pennsylvania, Rutgers University in New Jersey and Gustavus Adolphus Colleges in Minnesota.
• Maurice Liebman Memorial Prize from the Institute of Radio Engineers (now the Institute of Electrical and Electronics Engineers (IEEE)) in 1980.
• Shockley was named by Time Magazine as one of the 100 most influential people of the 20th century.
• In 2011, he was listed at #3 on the Boston Globe's MIT150 list of the top 150 innovators and ideas in the 150 year history of MIT.

Patents[link]

Shockley was granted over ninety US patents. Some notable ones are:

• US 2502488  "Semiconductor Amplifier". Applied for on Sept. 24, 1948; his first granted patent involving transistors.
• US 2569347  "Circuit element utilizing semiconductive material" His earliest applied for (June 26, 1948) patent involving transistors.
• US 2655609  "Bistable Circuits". Applied for on July 22, 1952; Used in computers.
• US 2787564  "Forming Semiconductive Devices by Ionic Bombardment". Applied for on Oct. 28, 1954; The diffusion process for implantation of impurities.
• US 3031275  "Process for Growing Single Crystals". Applied for on Feb. 20, 1959; Improvements on process for production of basic materials.
• US 3053635  "Method of Growing Silicon Carbide Crystals". Applied for on Sept. 26, 1960; Exploring other semiconductors.

Bibliography[link]

Prewar scientific articles by Shockley[link]

• An Electron Microscope for Filaments: Emission and Adsorption by Tungsten Single Crystals, R. P. Johnson and W. Shockley, Phys. Rev. 49, 436 - 440 (1936).
• Optical Absorption by the Alkali Halides, J. C. Slater and W. Shockley, Phys. Rev. 50, 705 - 719 (1936).
• Electronic Energy Bands in Sodium Chloride, William Shockley, Phys. Rev. 50, 754 - 759 (1936).
• The Empty Lattice Test of the Cellular Method in Solids, W. Shockley, Phys. Rev. 52, 866 - 872 (1937).
• On the Surface States Associated with a Periodic Potential, William Shockley, Phys. Rev. 56, 317 - 323 (1939).
• The Self-Diffusion of Copper, J. Steigman, W. Shockley and F. C. Nix, Phys. Rev. 56, 13 - 21 (1939).

Books by Shockley[link]

• Shockley, William – Electrons and holes in semiconductors, with applications to transistor electronics, Krieger (1956) ISBN 0-88275-382-7.
• Shockley, William and Gong, Walter A – Mechanics Charles E. Merrill, Inc. (1966).
• Shockley, William and Pearson, Roger – Shockley on Eugenics and Race: The Application of Science to the Solution of Human Problems Scott-Townsend (1992) ISBN 1-878465-03-1.

Books about Shockley[link]

• Joel N. Shurkin; Broken Genius: The Rise and Fall of William Shockley, Creator of the Electronic Age. New York: Palgrave Macmillan (2006) ISBN 1-4039-8815-3
• Michael Riordan and Lillian Hoddeson; Crystal Fire: The Invention of the Transistor and the Birth of the Information Age. New York: Norton (1997) ISBN 0-393-31851-6 pbk.
• Roger Pearson; Shockley on Eugenics and Race: The Application of Science to the Solution of Human Problems. Washington DC: Scott Townsend Publishers (1992) ISBN 1-878465-26-0 pbk.

References[link]

External links[link]

Wikimedia Commons has media related to: William Shockley

Wikiquote has a collection of quotations related to: William Shockley

• National Academy of Sciences biography
• Nobel biography
• Nobel Lecture
• PBS biography
• Gordon Moore. Biography of William Shockley Time Magazine
• Interview with Shockley biographer Joel Shurkin
• History of the transistor
• Simulation of a BJT in the Common Emitter Circuit
• Bipolar Transistors - The Transistor as a Switch - Active Region
• Lessons In Electric Circuits – Bipolar Junction Transistors
• EncycloBEAMia – Bipolar Junction Transistor
• Shockley and Bardeen-Brattain patent disputes
• Series of Slate.com Articles on the controversial sperm bank
• The genius factory
• William Shockley vs. Francis Cress-Welsing (Tony Brown Show, 1974)
• A Shockley website (shockleytransistor.com) has been established, using the company name, to honor Shockley and those who first processed silicon in Silicon Valley.
• Works by or about William Shockley in libraries (WorldCat catalog)

African American

Frederick Douglass · Barack Obama · Rosa Parks Condoleezza Rice · M. L. King, Jr. · Beyoncé Knowles Malcolm X · Oprah Winfrey · Booker T. Washington Michael Jordan · Harriet Tubman · Muhammad Ali
Total population
African American 42,020,743[1] (13.6% of the US population)
Regions with significant populations
Predominantly in the Southern United States and in urban areas within the country
Languages
American English · African American Vernacular English · Gullah language
Religion
Predominantly Protestant; also Roman Catholic, Muslim and agnostic
Related ethnic groups
Other Afro-American peoples of the Americas (especially Anglophones) Americo-Liberians · Sierra Leone Creole people Black Nova Scotians, Foreign-born Afro-Americans, Afro-Latin American view talk edit

African Americans^[2] (also referred to as Black Americans or Afro-Americans, and formerly as American Negroes) are citizens or residents of the United States that have ancestry from any of the native populations of Sub-Saharan Africa.^[3]

African Americans make up the single largest racial minority in the United States.^[4] Most African Americans are of West and Central African descent and are descendants of enslaved Africans within the boundaries of the present United States.^[5][6] However, some immigrants from African, Caribbean, Central American or South American nations, or their descendants, may be identified or self-identify with the term.^[3]

African-American history starts in the 16th century with African slaves who quickly rose up against the Spanish explorer Lucas Vázquez de Ayllón and progresses to the present day, with Barack Obama as the 44th and current President of the United States. Between those landmarks there have been events and issues, both resolved and ongoing, including slavery, racism, Reconstruction, development of the African-American community, participation in the great military conflicts of the United States, racial segregation, and the Civil Rights Movement.

History[link]

Slavery era[link]

The first African slaves arrived in the present-day United States as part of the San Miguel de Gualdape colony (most likely located in the Winyah Bay area of present-day South Carolina), founded by Spanish explorer Lucas Vázquez de Ayllón in 1526. The ill-fated colony was almost immediately disrupted by a fight over leadership, during which the slaves revolted and fled the colony to seek refuge among local Native Americans. De Ayllón and many of the colonists died shortly afterwards of an epidemic and the colony was abandoned, leaving the escaped slaves behind on North American soil.

In 1565, the colony of Saint Augustine in Florida, founded by Pedro Menendez de Aviles, became the first permanent European settlement in North America. It included an unknown number of free and enslaved Africans that were part of this colonial expedition.

The first recorded Africans in British North America (including most of the future United States) arrived in 1619 in Jamestown, Virginia. As English settlers died from harsh conditions, more and more Africans were brought to work as laborers. The Africans were likely treated as indentured servants, similar in legal position to poor English indenturees, who traded several years labor in exchange for passage to America.^[7] Africans could legally raise crops and cattle to purchase their freedom.^[8] They raised families, marrying other Africans and sometimes intermarrying with Native Americans or English settlers.^[9] By the 1640s and 1650s, several African families owned farms around Jamestown and some became wealthy by colonial standards.

An artist's conception of Crispus Attucks (1723–1770), the first "martyr" of the American Revolution.

The popular conception of a race-based slave system did not fully develop until the 18th century. The Dutch West India Company introduced slavery in 1625 with the importation of eleven black slaves into New Amsterdam (present-day New York City). All the colony's slaves, however, were freed upon its surrender to the British.^[10] Massachusetts was the first British colony to legally recognize slavery in 1641. It was not until 1662 that Virginia ruled that a slave mother's children would remain slaves.^[11]

The first black congregations and churches were organized before 1800 in both northern and southern cities following the Great Awakening. By 1775, Africans made up 20% of the population in the American colonies, which made them the second largest ethnic group after the English.^[12] During the 1770s, Africans, both enslaved and free, helped rebellious English colonists secure American Independence by defeating the British in the American Revolution.^[13] Africans and Englishmen fought side by side and were fully integrated.^[14] James Armistead, an African American, played a large part in making possible the 1781 Yorktown victory, which established the United States as an independent nation.^[15] Other prominent African Americans were Prince Whipple and Oliver Cromwell, who are both depicted in the front of the boat in George Washington's famous 1776 Crossing the Delaware portrait.

By 1860, there were 3.5 million enslaved African Americans in the United States due to the Atlantic slave trade, and another 500,000 African Americans lived free across the country.^[16] In 1863, during the American Civil War, President Abraham Lincoln signed the Emancipation Proclamation. The proclamation declared that all slaves in states which had seceded from the Union were free.^[17] Advancing Union troops enforced the proclamation with Texas being the last state to be emancipated in 1865.^[18]

Reconstruction and Jim Crow[link]

Jesse Owens shook racial stereotypes both with Nazis and segregationists in the USA at the 1936 Berlin olympics.

African Americans quickly set up congregations for themselves, as well as schools, community and civic associations, to have space away from white control or oversight. While the post-war reconstruction era was initially a time of progress for African Americans, in the late 1890s, Southern states enacted Jim Crow laws to enforce racial segregation and disenfranchisement.^[19] Most African Americans followed the Jim Crow laws, using a mask of compliance to prevent becoming victims of racially motivated violence. To maintain self-esteem and dignity, African Americans such as Anthony Overton and Mary McLeod Bethune continued to build their own schools, churches, banks, social clubs, and other businesses.^[20]

In the last decade of the 19th century, racially discriminatory laws and racial violence aimed at African Americans began to mushroom in the United States. These discriminatory acts included racial segregation—upheld by the United States Supreme Court decision in Plessy v. Ferguson in 1896^[21]—which was legally mandated by southern states and nationwide at the local level of government, voter suppression or disenfranchisement in the southern states, denial of economic opportunity or resources nationwide, and private acts of violence and mass racial violence aimed at African Americans unhindered or encouraged by government authorities.

Great Migration and Civil Rights Movement[link]

The desperate conditions of African Americans in the South that sparked the Great Migration of the early 20th century,^[22] combined with a growing African American community in the Northern United States, led to a movement to fight violence and discrimination against African Americans that, like abolitionism before it, crossed racial lines. The Civil Rights Movement from 1954 to 1968 was directed at abolishing racial discrimination against African Americans, particularly in the Southern United States. The March on Washington for Jobs and Freedom and the conditions which brought it into being are credited with putting pressure on President John F. Kennedy and Lyndon B. Johnson.

An African American boy outside of Cincinnati, Ohio in the 1940s

March on Washington, August 28, 1963, shows civil rights and union leaders

Johnson put his support behind passage of the Civil Rights Act of 1964 that banned discrimination in public accommodations, employment, and labor unions, and the Voting Rights Act (1965), which expanded federal authority over states to ensure black political participation through protection of voter registration and elections. By 1966, the emergence of the Black Power movement, which lasted from 1966 to 1975, expanded upon the aims of the Civil Rights Movement to include economic and political self-sufficiency, and freedom from white authority.^[23]

Post-Civil Rights era[link]

Politically and economically, blacks have made substantial strides during the post-civil rights era. In 1989, Douglas Wilder became the first African-American elected governor in U.S. history. There is currently one black governor; governor Deval Patrick of Massachusetts. Clarence Thomas became the second African-American Supreme Court Justice. In 1992 Carol Moseley-Braun of Illinois became the first black woman elected to the U.S. Senate. There were 8,936 black officeholders in the United States in 2000, showing a net increase of 7,467 since 1970. In 2001 there were 484 black mayors.

On November 4, 2008, Democratic Senator Barack Obama defeated Republican Senator John McCain to become the first African American to be elected President. At least 95 percent of African-American voters voted for Obama.^[24][25] He also received overwhelming support from young and educated whites, a majority of Asians, Hispanics,^[26] and Native Americans^{[27][not in citation given]} picking up a number of new states in the Democratic electoral column.^[24][25] Obama lost the overall white vote, although he won a larger proportion of white votes than any previous nonincumbent Democratic presidential candidate since Jimmy Carter.^[28] The following year Michael S. Steele was elected the first African-American chairman of the national Republican Party.^[29]

Demographics[link]

African Americans as a percentage of total population, 2000.

In 1790, when the first U.S. Census was taken, Africans (including slaves and free people) numbered about 760,000—about 19.3% of the population. In 1860, at the start of the Civil War, the African American population had increased to 4.4 million, but the percentage rate dropped to 14% of the overall population of the country. The vast majority were slaves, with only 488,000 counted as "freemen". By 1900, the black population had doubled and reached 8.8 million. In 1910, about 90% of African Americans lived in the South, but large numbers began migrating north looking for better job opportunities and living conditions, and to escape Jim Crow laws and racial violence. The Great Migration, as it was called, spanned the 1890s to the 1970s. From 1916 through the 1960s, more than 6 million black people moved north. But in the 1970s and 1980s, that trend reversed, with more African Americans moving south to the Sun Belt than leaving it.

The following table of the African American population in the United States over time shows that the African American population, as a percentage of the total population, declined until 1930 and has been rising since then.