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Intellectual quotients of a population represented in a normal distribution

A quotient or intelligence quotient (IQ; German: Intelligenzquotient, IQ) is a result obtained on a standardized test that attempts to measure human intelligence. Given the abstract nature of the concept of intelligence, an IQ is no more than an estimate.

IQ follows a normal distribution with a median of 100 and a standard deviation of 15, so that two-thirds of the population have an IQ between 85 and 115, and 2.5% have an IQ of more than 130 or less than 70.

Some authors consider that the human brain is complex enough to not be able to measure intelligence with a single factor, but others consider that it has great predictive value in terms of academic or work performance. Recently, Nassim Taleb, who considers IQ as an example of pseudoscience, denied its statistical validity. As a partial response to these criticisms, intelligence tests tend to be more complex and provide other estimators, apart from IQ, that need to be assessed. Initially, the IQ was obtained by dividing a person's mental age (obtained after taking tests or non-standardized tests) by their chronological age and multiplying the result by 100. However, in the second half of the 20th century, this method it was replaced by the design of standardized tests that directly yielded the score of this estimator.

Terminology

Until the 22nd edition of the Dictionary of the Spanish language of the RAE, published in 2001, the term «coefficient» was included with its own entry, and from March 2012, date In which the 1,697 modifications approved since September 2007 are incorporated, the Royal Spanish Academy added to the electronic page of the advance of the twenty-third edition of its Dictionary, as an "amended article", the term "quotient", and thus collected the use that occurs in the field of psychology in Spanish since at least 1978. It should be noted that the two terms have coexisted, even together on the same page, in various specialized publications.

History

For many years, attempts have been made to classify people into various intelligence categories by observing their behavior in everyday life. That was even before IQ tests were invented. Those other forms of behavioral observation are still important in validating rankings based primarily on intelligence test results.

The term intelligence quotient was used for the first time by the Wroclaw University psychologist William Stern in 1912. Its purpose was to name a new method for scoring the results of the first tests. intelligence tests for children, developed by Alfred Binet and Théodore Simon in the early XX century. The French psychologists Alfred Binet and Théodore Simon published, in 1905, the test called Mental Age. The score on the scale of this Binet-Simon test would reveal the child's mental age. The measure of intelligence consisted of dividing mental age by chronological age and multiplying the result by 100, resulting in the aforementioned quotient. The American psychologist Lewis Terman, from Stanford University, reviewed the Binet test -Simon, and the name was changed to the Stanford-Binet Intelligence Scale (1916). It became the most popular test in the United States for decades.

Although the term IQ is still commonly used to refer to an intelligence test result, the score on tests used today, such as the Wechsler Intelligence Scale for Adults, is based on the projection of the subject's measured range in a Gaussian bell formed by the distribution of possible values for his age group, with a central value (mean intelligence) of 100 and a standard deviation of 15. In general terms, values greater than 100 are above the mean, while values less than 100 are below the mean, but the standard deviation makes people with scores between 85 and 115 considered to be within the range. For example, a person with an IQ of 90 is below the average, but within the expected deviation. Also, different tests may have different standard deviations.

Mean scores for many populations have tended to rise by an average of three points per decade since the early [[20th century|20th century]], with most of the increase accumulating in the lower half of the IQ curve; this phenomenon is known as the Flynn effect. There is controversy as to whether this steady increase is caused by a real increase in intellectual abilities in such populations, or rather due to methodological problems with past or present testing.

G-factor

Today, different types of intelligence tests are based on different theoretical frameworks and conceptions of intelligence. However, it is common for these measurement tools to include scores on specific domains of competence (language, spatial intelligence, etc.) at various levels of abstraction, and also offer a G Factor, as a value that summarizes the general intelligence of the individual.

In 1904 the British psychologist Charles Spearman made the first factor analysis of the correlations between measures of cognitive ability. Spearman found that children's performance scores in seemingly unrelated subjects were positively correlated with all other subjects. From this observation he highlighted that these correlations reflected the influence of general mental ability on other tasks not related to school. Thus, an explanatory model of intelligence called the bifactorial theory of intelligence was created. This theory proposes the existence of a general factor (Factor g) of cognitive ability and some specific factors (S), which are understood as abilities and aptitudes that are present in certain areas of life. These two components are considered different, but not independent, since Factor G is the most important, it has a generic action on individual cognitive abilities. However, this point of view is not universally accepted; there are other models of human intelligence.^{[citation needed]}

Today's models of intelligence are represented as a hierarchy of three levels, where the primary skills (performance) are located at the bottom, and the secondary skills (visual and auditory perception, cognitive speed, etc.) in the middle part., Crystallized Intelligence and Fluid Intelligence, among others) and, finally, at the top is the G Factor, called General Intelligence.

Currently, the field of behavioral genetics research has established that Factor G is hereditary and would fundamentally depend on the genetic load.

American Psychological Association Agreements on Intelligence

In 1994, a statement was published in the Wall Street Journal with 25 basic points on the scientific study of intelligence, endorsed by more than 50 scientists from different backgrounds. The purpose of this publication was to counter the misconceptions and myths spread by the media after the publication of the book The Bell Curve, accused of lacking a scientific basis in any of its statements. Here are some of the agreements regarding intelligence quotient (IQ) that were proposed as points on which to continue the debate:

Intelligence is not the same as knowledge, but a general capacity that allows solving problems, reasoning, planning, thinking abstractly, understanding complex ideas and learning from experience.
Intelligence can be measured through tests, which constitute a reliable and accurate measurement method.
There are tests of many types, but they all measure the same. Some are culturally mediated (requiring of specific learning or prior knowledge) and others contemplate non-mediated "universal" concepts.
The distribution according to the performance in the tests is represented by a standard distribution, in which most people are around the central values (CI=100); few are far removed either above or below this central value.
The tests do not present cultural biases that harm certain ethnic groups.
The intellectual level relates to performance in social, educational or occupational fields.
A high intellectual level facilitates the performance of daily activities (increasing their importance in complex tasks), but does not guarantee success or failure in the life trajectory.
Differences in academic performance do not depend solely on the IQ, but intelligence is often the most important factor.
The inheritance of intelligence ranges from 0.4 to 0.8 correlation (scaling from 0 to 1), with an important influence of the environment.
It is still unknown how to manipulate intelligence permanently.
Ethnic-racial differences are significant at the same socio-economic level, but the cause is unknown.
An increase in the results of intelligence tests over the years is detected due to various environmental effects. This phenomenon is called Flynn Effect.

It is important to consider the date and the geography in which these questions are raised (North American society in the late 1990s), so its generalization must be done with caution. The report also exposed a series of unanswered questions that formed a large part of the scientific research agenda on intelligence in the XXI century. Among these we find the "mechanisms of influence of genes on intelligence", "the explanation of the increase in genetic influence with age", "what are the most influential environmental factors, the role played by nutrition or schooling in the level of intelligence or why there are differences in median scores between different social groups.

Genetics and environment

Heredity of intelligence

We understand IQ heritability as the proportion of variance in a trait that is attributable to genotype within a defined population in a specific environment. Heritability measures how much of that variation is caused by genetics, and the values we obtain are variable throughout our lives, since they directly coincide with environmental effects. The official figure for the heritability of IQ according to a report by from the American Psychological Association, it is 0.45 for children and rises to around 0.75 for adolescents and adults. Heritability therefore becomes important as we age, and not the other way around, as we might think based on experience and learning. However, members of a family have environmental aspects in common. This shared environment represents between 0.25 and 0.35 of the variation of the IQ in childhood; later, when passing into adolescence, this value tends to 0.

The environment

According to William Dickens and James R. Flynn, high IQ genes initiate a feedback loop between the individual and the environment, where children with greater mental abilities seek more stimulating environments that end up increasing their IQ. The Flynn effect can be explained for these reasons by relating the increase in environmental stimuli to the rise in the overall mean IQ.

Tests

Psychometrics is the scientific discipline that is part of the behavioral science methodology and is directly related to the field of psychological measurement. It is a science whose purpose is to measure the psychological aspects of a person, such as personality traits, abilities, mental abilities, general knowledge and attitude. Traditionally, tests of intelligence measures have been criticized for being culturally mediated. That is, it was believed that they had an important cultural load that required prior learning by the subjects. Today, they tend to be culturally impartial.

The first psychometric tests were built to measure intelligence through procedures that evaluated the intelligence quotient of individuals, a measure that was supposed to approximate the construct of intelligence. Generally, the measures are obtained through statistical techniques based on correlation, such as factor analysis or linear regression. On a practical level, psychometrics makes intensive use of calculations and statistical analysis, assigning numbers and identifying attributes. physical and psychological. Variable difficulty and theme tests that measure the ability to perform a task through a score are considered. These include verbal analogies, rotation or spatial orientation, numerical computation, and knowledge of language.

Currently, there are various tests that allow obtaining a measure of aptitudes of a general or global level of intelligence: Stanford-Binet test, Wechsler scales, McCarthy scales, Raven's Progressive Matrices test, Dominoes test, K -ABC, DAT-5, Factor G test.

Measurements: IQ Scores and Ranks

IQ scores are used in many different contexts: predictors of school performance, indicators of special educational needs, predictors of job performance, or by sociologists who study the distribution of intelligence in populations and the relationships between intelligence and other variables. Some educators and psychologists present the following classification to describe different levels of intellectual giftedness, with IQ as a reference point:

No cognitive ability IQ 0-4

Less than 0.000001% have such an IC. The person with this disorder cannot read, speak, communicate, much less write. You need psychological help. Most were and are examples of the so-called "wild children", who were and are raised on the margins of society in certain countries.

Profound Cognitive Impairment IQ 5-19

Includes approximately 1-2% of people with cognitive disabilities. Most individuals with this diagnosis have an identified neurological disease that explains their cognitive impairment. During the first years, they develop considerable alterations in sensory-motor functioning. Optimal development can be predicted in a highly structured environment with constant support and supervision, as well as establishing an individualized relationship with the educator. Motor development and communication and personal care skills can improve if you undergo proper training. Some of them get to perform simple tasks in closely supervised and protected institutions.

Severe Cognitive Disability IQ 20-34

Includes 3-4% of individuals with cognitive disabilities. During the early years of childhood, there is little or no acquisition of communicative language. During school age, they can learn to speak and can learn elementary personal care skills. They benefit only to a limited extent from the teaching of pre-academic subjects such as familiarity with the alphabet and simple calculation, but they can master certain skills such as learning to read globally some essential words for their autonomy and independence. Adults may be able to perform simple tasks closely supervised in institutions. For the most part, they adjust well to life in the community, unless they suffer from an associated disability that requires specialized care or other assistance.

Moderate cognitive impairment IQ 35-54

Moderate cognitive disability roughly equates to the pedagogical category of "moldable." This group constitutes about 10% of the entire population with cognitive disabilities. They acquire communication skills during the early years of childhood. They acquire job training and, with moderate supervision, may acquire skills for their own personal care. They may also benefit from remediation in social and employment skills, but are unlikely to progress beyond a second level in school subjects. They can learn to move independently through places that are familiar to them. Most of them are capable of carrying out unskilled or semi-skilled work, always under supervision, in sheltered workshops or in the general labor market. They adapt well to community life, usually in supervised institutions.

Mild Cognitive Disability IQ 55-69

This is the name given to people who go through the “educable stage”. They are about 87% of people affected by the disorder. They usually develop social and communication skills during the preschool years (0-5 years). They have minimal impairments in sensorimotor areas and are often indistinguishable from other children without cognitive impairment until later ages. They acquire adequate social and work skills for minimal autonomy, but may need supervision, guidance and assistance, especially in situations of unusual social or economic stress. With adequate support, subjects with mild cognitive disabilities live without problems in the community, either independently or in supervised establishments.

Borderline intelligence IQ 70-84

One in nine people occupies this rank. Contrary to brilliant intelligence, retardation presents its own characteristics: Being below average in adults is also responsible for some children failing at school. It's only a slight delay, so it shouldn't be confused as asynchronous. It has more than 2/7 of the world's population in this range, corresponding oppositely with the so-called "brilliant intelligence" (CI = 115-129).

Below average IQ 85-99

They present an intelligence below the value of 100, but in most cases such a difference is not perceptible, especially since most people are close to the average value. They do not present problems during their childhood, nor difficulties to integrate in general. A little less than 12% of the world population is in this status.

Mean Established IQ 100

Most of the population is in this range as shown by the Gaussian bell graph. It is a non-absolute value on the large scale. Not absolute because that same value increases 3 points per decade, so that it always gives values of 100. The reason for this is that progress and development in the world are causing many societies to progressively ascend in the stratification, to get out of the status of poverty, do not suffer famine or malnutrition, diseases, among other things, that make the average intelligence of the human being increase gradually, consequently bring about change. Anyway, it's like the middle ground between retardation, mental disorder, and giftedness classes. It is the midpoint on which the entire scale is based. For example: A person is just 15 years old and knows that he has the same amount of mental age. The result comes out alone: 15/15=1. And now we have to multiply it by 100, because it is the average value of the quotient. 1 × 100 = 100. In other words, that person has a balance between his biological age and her mental age. They tend to be absent from psychological problems and also do not have sleep problems: They sleep 9 hours a day. Almost 3% of the population has an IQ of 100, taking into account that the scale extends from 0 (null IQ) to 201 (probable maximum on the Stanford-Binet scale, counting the maximum rarity of one in seven billion). population).

Above Average IQ 101-114

It is a range that reaches approximately 3 out of 10 people. It corresponds to a person with an ability that is not noticeably detectable as "smarter," but it is a significant value, especially the further up the scale you go.

Brilliant intelligence CI 115-129

This corresponds to approximately 13% of people. It presents an intelligence superior to the others. Most professions and performance roles are in this range. The median for most people with highest intellectual quotient degrees in the Western world hovers around 125 IQ points.

Intellectual giftedness IQ 130-144

Distribution curve in the Wechsler scale of a normal population with an average of 100 (red) compared to the distribution curve of the 301 geniuses of Catharine Cox of 1926 (blue). It has a relevant correction made after the Flynn effect to date since the publication of the book.

Intellectual genius IQ 145-155

Geniuses are those who have an IQ equal to or greater than 145 (generally), and represent 0.1% (1 in 1000) of the population. That is to say, that its result is in the extreme right part of the curve of results (a Gaussian bell). It is the limit that distinguishes the common professional with the highest intellectual rank from the average among scientists and socially misunderstood geniuses. Simonton and David Wechsler point out that around 145 IQ points a radical way of thinking with respect to other groups begins to emerge, at the same time that other types of derived psychological problems increase.

Superior intelligence CI 156-174

See also: High intellectual capacities

Has a rarity on the Stanford-Binet Intelligence Scale, Fourth Revision, (SB4 16SD) of one in three thousand five hundred people (0.03% of the population). This group is characterized by a radically different way of thinking, and often suffer from problems such as low academic or work performance syndrome, dyssynchrony syndrome, as well as emotional problems or personality disorders. However, this is likely to be the effect and not the cause, since due to its rarity and distance from the mean it is difficult for most to understand its way of thinking. For Simonton this phenomenon is due to the fact that when there is a difference of 20 IQ points between the sender and the receiver there will not be a full understanding.

Exceptional intelligence CI 175-189

Only one in 700,000 people in the world reaches such intelligence (SB4 16SD). For this reason, it is possible that even a person can begin to read under three years of age. Generally, you can learn languages with relative ease, and you have a great command of your own language. It is a gift to possess such an intellect. People feel great emotions, and are very sentimental when facing certain situations. They reach a school performance of around 96/100, and in the educable stage their intelligence is very remarkable as "honorable".^{[citation required]}

Deep Intelligence CI 190-201

Approximately one person out of 18 million is capable of reaching such a high score (SB4 16SD). It is a much higher intelligence, but it is also difficult to reach this range: approximately 0.00000005% of all people the world have such a quotient.

Intelligence greater than 201

Numbers greater than this number are unlikely or possibly a hoax, since the rarity for 201 on the Stanford-Binet scale (SB4 16SD) or 195 on the Wechsler scale (15SD) is one in eight billion people, and Humanity barely exceeds seven billion people.

However, in this CI there are people with very interesting stories, like William James Sidis, Marilyn vos Savant and Christopher Hirata.

Social impact

Academic Performance and IQ

Throughout the academic period, from elementary school to postgraduate courses, there is a relationship between student performance and their scores on IQ tests. It is observed that this relationship decreases in intensity over time: • 6-12 years (primary): the correlation is 0.7 • 12-18 years (secondary): the correlation becomes 0.5 • 18-22 years (university): a decrease to 0.4 is observed • More than 22 years (postgraduate): the correlation decreases to 0.3.

Job Performance and IQ

The validity of IQ as a predictor of job performance is greater than zero for all jobs studied to date, but varies with the type of job (from 0.2 to 0.6). IQ is more related to reasoning and less to motor function; IQ test scores predict performance scores in all occupations. For highly qualified activities, lower IQ scores are more prone to encounter job obstacles, but this is not the case in minimally qualified activities where motor performance (strength, resistance, coordination...) would have more weight.

Crime and IQ

Arthur Jensen, in his book The g Factor: The Science of Mental Ability (1998), cites data showing that, regardless of social class, race, or family dysfunction, people with IQs between 70 and 90 have higher crime rates than people with IQs below or above this range. In addition, it is explained that school failure shows a high correlation with criminal behavior, being one of its best predictors.

The 1995 report of the American Psychological Association (APA), known as "Intelligence: Knowns and Unknowns," indicated that the correlation between IQ and delinquency is –0.20. That means that the explained variance is less than 4% and the causal links may be indirect.

The Flynn Effect

Main article: Flynn Effect

It is named after James R. Flynn, a New Zealand political scientist who discovered that worldwide IQ scores were slowly rising at the rate of three IQ points per decade (Flynn, 1999). Explanations that have been proposed have included better nutrition, a trend toward smaller families, better education, greater complexity in the environment, and heterosis (Mingroni, 2004). However, tests are occasionally renormalized to obtain mean score values of 100, as, for example, in the WISC-R (1974), WISC-III (1991), and WISC-IV (2003). Therefore, it is difficult to compare IQ scores whose measurement is several years away in time.

There is recent evidence that shows that the upward trend in intelligence test scores has subsided in some first world countries. In 2004, Jon Martin Sundet (of the University of Oslo) and some collaborators published an article documenting intelligence test scores administered to Norwegian recruits between the 1950s and 2002, showing that the increase in general intelligence test scores was stopped after the mid-1990s, and even decreased on the numerical reasoning subtest.

Thomas W. Teasdale (University of Copenhagen) and David R. Owen (Brooklyn College, New York City) found similar results in Denmark, where IQ test results showed no increase over time. the nineties.

There are also indications from the UK that IQ test scores are not always going up. Michael Shayer (a psychologist at King's College, University of London) and two colleagues reported that performance on physics reasoning tests given to British secondary school adolescents declined considerably between 1976 and 2003.

Age and IQ

IQ can change throughout our lives, especially in childhood. Despite these variations, the score follows very similar margins until the beginning of adulthood, where it would begin to slowly decrease. This fact has subsequently been attributed by various researchers to a greater extent to the Flynn effect and its collateral consequences, than to the aging of the individual himself.

In terms of intelligence and variability, following the model proposed by Raymond Cattell, we can distinguish two types: fluid intelligence would be the one that varies the most over time, and crystallized intelligence that remains stable throughout our life. life. To empirically study the changes in intelligence associated with age, there are two basic study designs: cross-sectional, which consists of evaluating groups of different ages at the same time point; and the longitudinal one that consists of evaluating a group of people of the same age at different moments of their lives. In addition to these two types, we find a third study model that combines the previous two, called Time-lag or sequential-transversal, which consists of evaluating different groups of people by ages at different points in time (Ex: people in their 20s, 30s, and 40s in the 1950s, 1960s, and 1970s).

Controversy

Researchers at Western Canada University and the Science Museum in London conducted "the largest study to measure intelligence" ever conducted, concluding that the IQ test is highly misleading. The objective of the study was to investigate whether a single number can really measure cognitive abilities, and reflect whether it can establish differences in different cognitive abilities. According to these researchers, brain scan tests can verify three fundamental cognitive components —short-term memory, reasoning, and verbal ability— that correspond to three different patterns of neural activity.

The results of the study suggest that IQ tests are "fundamentally flawed" because they fail to take into account "the complex nature of the human intellect with all its various components." Intelligence is made up of different circuits and some people can excel in one area of intelligence and not in another. This would be the case, for example, of people with fantastic language skills and a brilliant memory, but with little reasoning ability or vice versa. The researchers conclude: “Our results once and for all disprove the idea that a single measure of intelligence, such as IQ, is sufficient to account for all the differences in cognitive ability that we see between people; the human brain is the most complex object known, so far, and the idea that there is only one measure of intelligence could be wrong."

It is important to clarify that the intelligence quotient cannot be used as a synonym of intelligence, since it is only an estimator of it. However, most non-professional reading makes the mistake of taking it as the same thing. For this reason, the reader is advised that every time he reads or hears something about IQ, he makes sure if he is talking about this intelligence estimator or intelligence itself.

It has been shown that intelligence is related to factors such as the probability of suffering from certain diseases, the social status of parents (due to access to better education, food and health) and, substantially, the intelligence of parents. Although the mechanisms of intelligence inheritance have been investigated for almost u, there is still controversy regarding the extent to which intelligence is hereditary, and the mechanisms of such inheritance are still a matter of debate.

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