• What does my IQ mean ?
• What is intelligence ?
• What do we know about Intelligence ?
• Are there differences in IQ among countries ?
• Are there differences in IQ between the sexes ?
• Is IQ determined by genes or by environment ?
• What is Mensa ?
• What is UberMens ?
• What is emotional intelligence ?

topWhat does my IQ mean?

IQ are measured on a scale that goes from 45 to 155. An IQ of 100 is the average. If your IQ is higher than 100 you are more intelligent than most people. If your IQ is lower than 100 you are less intelligent than most people.

In the figure below you see that the majority of the population has an IQ of around 100. There are few people who have an IQ of less than 85 and also few who have one over 115.

topWhat is intelligence ?

There are many definitions of intelligence. The American Psychological Association defines it as follows:

Individuals differ from one another in their ability to understand complex ideas, to adapt effectively to the environment, to learn from experience, to engage in various forms of reasoning, to overcome obstacles by taking thought. Although these individual differences can be substantial, they are never entirely consistent: a given person’s intellectual performance will vary on different occasions, in different domains, as judged by different criteria. Concepts of "intelligence" are attempts to clarify and organize this complex set of phenomena. Although considerable clarity has been achieved in some areas, no such conceptualization has yet answered all the important questions and none commands universal assent. Indeed, when two dozen prominent theorists were recently asked to define intelligence, they gave two dozen somewhat different definitions.

A second definition of intelligence comes from "Mainstream Science on Intelligence", which was signed by 52 intelligence researchers in 1994:

A very general mental capability that, among other things, involves the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly and learn from experience. It is not merely book learning, a narrow academic skill, or test-taking smarts. Rather, it reflects a broader and deeper capability for comprehending our surroundings—"catching on", "making sense" of things, or "figuring out" what to do.

topWhat do we know about intelligence ?

There are many rumours about intelligence and many falsities and half-truth written about it. To end this, in 1994 prominent researchers on intelligence came together an published together the factual knowledge about intelligence. The following are their conclusions about scientific knowledge about intelligence.

The Meaning and Measurement of Intelligence

1. Intelligence is a very general mental capability that, among other things, involves the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly and learn from experience. It is not merely book learning, a narrow academic skill, or test-taking smarts. Rather, it reflects a broader and deeper capability for comprehending our surroundings--"catching on," "making sense" of things, or "figuring out" what to do.

2. Intelligence, so defined, can be measured, and intelligence tests measure it well. They are among the most accurate (in technical terms, reliable and valid) of all psychological tests and assessments. They do not measure creativity, character personality, or other important differences among individuals, nor are they intended to.

3. While there are different types of intelligence tests, they all measure the same intelligence. Some use words or numbers and require specific cultural knowledge (like vocabulary). Others do not, and instead use shapes or designs and require knowledge of only simple, universal concepts (many/few, open/closed, up/down).

4. The spread of people along the IQ continuum, from low to high, can be represented well by the bell curve (in statistical jargon, the "normal curve"). Most people cluster around the average (IQ 100). Few are either very bright or very dull: About 3% of Americans score above IQ 130 (often considered the threshold for "giftedness"), with about the same percentage below IQ 70 (IQ 70-75 often being considered the threshold for mental retardation).

5. Intelligence tests are not culturally biased against American blacks or other native-born, English-speaking peoples in the U.S. Rather, IQ scores predict equally accurately for all such Americans, regardless of race and social class. Individuals who do not understand English well can be given either a nonverbal test or one in their native language.

6. The brain processes underlying intelligence are still little understood. Current research looks, for example, at speed of neural transmission, glucose (energy) uptake, and electrical activity of the brain, uptake, and electrical activity of the brain.

Group Differences

7. Members of all racial-ethnic groups can be found at every IQ level. The bell curves of different groups overlap considerably, but groups often differ in where their members tend to cluster along the IQ line. The bell curves for some groups (Jews and East Asians) are centered somewhat higher than for whites in general. Other groups (blacks and Hispanics) are centered somewhat lower than non-Hispanic whites.

8. The bell curve for whites is centered roughly around IQ 100; the bell curve for American blacks roughly around 85; and those for different subgroups of Hispanics roughly midway between those for whites and blacks. The evidence is less definitive for exactly where above IQ 100 the bell curves for Jews and Asians are centered.

Practical Importance

9. IQ is strongly related, probably more so than any other single measurable human trait, to many important educational, occupational, economic, and social outcomes. Its relation to the welfare and performance of individuals is very strong in some arenas in life (education, military training), moderate but robust in others (social competence), and modest but consistent in others (law-abidingness). Whatever IQ tests measure, it is of great practical and social importance.

10. A high IQ is an advantage in life because virtually all activities require some reasoning and decision-making. Conversely, a low IQ is often a disadvantage, especially in disorganized environments. Of course, a high IQ no more guarantees success than a low IQ guarantees failure in life. There are many exceptions, but the odds for success in our society greatly favor individuals with higher IQs.

11. The practical advantages of having a higher IQ increase as life settings become more complex (novel, ambiguous, changing, unpredictable, or multifaceted). For example, a high IQ is generally necessary to perform well in highly complex or fluid jobs (the professions, management): it is a considerable advantage in moderately complex jobs (crafts, clerical and police work); but it provides less advantage in settings that require only routine decision making or simple problem solving (unskilled work).

12. Differences in intelligence certainly are not the only factor affecting performance in education, training, and highly complex jobs (no one claims they are), but intelligence is often the most important. When individuals have already been selected for high (or low) intelligence and so do not differ as much in IQ, as in graduate school (or special education), other influences on performance loom larger in comparison.

13. Certain personality traits, special talents, aptitudes, physical capabilities, experience, and the like are important (sometimes essential) for successful performance in many jobs, but they have narrower (or unknown) applicability or "transferability" across tasks and settings compared with general intelligence. Some scholars choose to refer to these other human traits as other "intelligences."

Source and Stability of Within-Group Differences

14. Individuals differ in intelligence due to differences in both their environments and genetic heritage. Heritability estimates range from 0.4 to 0.8 (on a scale from 0 to 1), most thereby indicating that genetics plays a bigger role than does environment in creating IQ differences among individuals. (Heritability is the squared correlation of phenotype with genotype.) If all environments were to become equal for everyone, heritability would rise to 100% because all remaining differences in IQ would necessarily be genetic in origin.

15. Members of the same family also tend to differ substantially in intelligence (by an average of about 12 IQ points) for both genetic and environmental reasons. They differ genetically because biological brothers and sisters share exactly half their genes with each parent and, on the average, only half with each other. They also differ in IQ because they experience different environments within the same family.

16. That IQ may be highly heritable does not mean that it is not affected by the environment. Individuals are not born with fixed, unchangeable levels of intelligence (no one claims they are). IQs do gradually stabilize during childhood, however, and generally change little thereafter.

17. Although the environment is important in creating IQ differences, we do not know yet how to manipulate it to raise low IQs permanently. Whether recent attempts show promise is still a matter of considerable scientific debate.

18. Genetically caused differences are not necessarily irremediable (consider diabetes, poor vision, and phenalketonuria), nor are environmentally caused ones necessarily remediable (consider injuries, poisons, severe neglect, and some diseases). Both may be preventable to some extent.

Source and Stability of Between-Group Differences

19. There is no persuasive evidence that the IQ bell curves for different racial-ethnic groups are converging. Surveys in some years show that gaps in academic achievement have narrowed a bit for some races, ages, school subjects and skill levels, but this picture seems too mixed to reflect a general shift in IQ levels themselves.

20. Racial-ethnic differences in IQ bell curves are essentially the same when youngsters leave high school as when they enter first grade. However, because bright youngsters learn faster than slow learners, these same IQ differences lead to growing disparities in amount learned as youngsters progress from grades one to 12. As large national surveys continue to show, black 17- year-olds perform, on the average, more like white 13-year-olds in reading, math, and science, with Hispanics in between.

21. The reasons that blacks differ among themselves in intelligence appear to be basically the same as those for why whites (or Asians or Hispanics) differ among themselves. Both environment and genetic heredity are involved.

22. There is no definitive answer to why IQ bell curves differ across racial-ethnic groups. The reasons for these IQ differences between groups may be markedly different from the reasons for why individuals differ among themselves within any particular group (whites or blacks or Asians). In fact, it is wrong to assume, as many do, that the reason why some individuals in a population have high IQs but others have low IQs must be the same reason why some populations contain more such high (or low) IQ individuals than others. Most experts believe that environment is important in pushing the bell curves apart, but that genetics could be involved too.

23. Racial-ethnic differences are somewhat smaller but still substantial for individuals from the same socioeconomic backgrounds. To illustrate, black students from prosperous families tend to score higher in IQ than blacks from poor families, but they score no higher, on average, than whites from poor families.

24. Almost all Americans who identify themselves as black have white ancestors-the white admixture is about 20%, on average--and many self-designated whites, Hispanics, and others likewise have mixed ancestry. Because research on intelligence relies on self- classification into distinct racial categories, as does most other social-science research, its findings likewise relate to some unclear mixture of social and biological distinctions among groups (no one claims otherwise).

topAre there difference in IQ among countries ?

Though not socially acceptable to say in public, in fact there seems to be clear evidence that there are substantial differences in IQ among countries even accounting for differences in education, upbringing and other factors. The map below shows measured IQ among different countries.

≤65        70        75        80        85        90        95        100        ≥105        N/A

topAre there differences in IQ between the sexes ?

Sex and intelligence research investigates differences in the distributions of cognitive skills between men and women. This research employs experimental tests of cognitive ability, which take a variety of forms, including written tests like the SAT. Research focuses on differences in individual skills as well as overall differences in general cognitive ability, which is often called g. IQ tests, specially designed to measure cognitive ability, usually test a variety of skills, and IQ scores are often used as a measure of g.

The populations of men and women differ on average in how well they perform on some of these skill tests, but do equally well on other tests. For example, women tend to score higher on certain verbal and memory tests, whereas men tend to score higher on spatial tests, particularly mental spatial rotations.

While these results are relatively uncontroversial, the question of whether men and women differ on average in g is a matter of debate among experts. Most recent studies unambiguously find that men as a population are more varied than women in g (i.e. they have a higher variance and therefore there are more men than women at the extremes of ability). Previously the opposite had been thought as evidenced by the variability hypothesis.

However, determining whether men and women differ on average has been more difficult. It is easy to design an IQ test in which either males or females score higher on average, by selecting different tests or giving them different weights, so the question boils down to which weights the different tests should have for the g factor.

The primary reason for expecting that men will have higher average g than women is the male advantage in brain size. Resolving this question requires the use of sophisticated statistical techniques to extract g from the results of IQ tests. Some studies find an average male advantage in g, but most do not.

topWhat is emotional intelligence ?

Emotional Intelligence (EI), often measured as an Emotional Intelligence Quotient (EQ), describes an ability , capacity, or skill to perceive, assess, and manage the emotions of one's self , of others, and of groups . It is a relatively new area of psychological research. The definition of EI is constantly changing.

Defining emotional intelligence

There are a lot of arguments about the definition of EI, arguments that regard both terminology and operationalizations . The first published attempt toward a definition was made by Salovey and Mayer (1990) who defined EI as “the ability to monitor one's own and others' feelings and emotions, to discriminate among them and to use this information to guide one's thinking and actions”

Despite this early definition, there has been confusion regarding the exact meaning of this construct. The definitions are so varied, and the field is growing so rapidly, that researchers are constantly amending even their own definitions of the construct. Up to the present day, there are three main models of EI:

• Ability-based EI models

• Mixed models of EI

• Trait EI models

The ability - based model

Salovey and Mayer's conception of EI strives to define EI within the confines of the standard criteria for a new intelligence. Following their continuing research, their initial definition of EI was revised to: "The ability to perceive emotion, integrate emotion to facilitate thought, understand emotions, and to regulate emotions to promote personal growth".

The ability based model views emotions as useful sources of information that help one to make sense of and navigate the social environment . The model proposes that individuals vary in their ability to process information of an emotional nature and in their ability to relate emotional processing to a wider cognition . This ability is seen to manifest itself in certain adaptive behaviors.

The model proposes that EI includes 4 types of abilities:

Perceiving emotions - the ability to detect and decipher emotions in faces, pictures, voices, and cultural artifacts - including the ability to identify one’s own emotions. Perceiving emotions represents a basic aspect of emotional intelligence, as it makes all other processing of emotional information possible.

Using emotions - the ability to harness emotions to facilitate various cognitive activities, such as thinking and problem solving. The emotionally intelligent person can capitalize fully upon his or her changing moods in order to best fit the task at hand.

Understanding emotions - the ability to comprehend emotion language and to appreciate complicated relationships among emotions. For example, understanding emotions encompasses the ability to be sensitive to slight variations between emotions, and the ability to recognize and describe how emotions evolve over time.

Managing emotions - the ability to regulate emotions in both ourselves and in others. Therefore, the emotionally intelligent person can harness emotions, even negative ones, and manage them to achieve intended goals.

Mixed models of EI

The Emotional Competencies (Goleman) model

The EI model introduced by Daniel Goleman focuses on EI as a wide array of competencies and skills that drive managerial performance, measured by multi-rater assessment and self-assessment (Bradberry and Greaves, 2005). In Working with Emotional Intelligence (1998), Goleman explored the function of EI on the job, and claimed EI to be the strongest predictor of success in the workplace, with more recent confirmation of these findings on a worldwide sample seen in Bradberry and Greaves, "The Emotional Intelligence Quick Book" (2005).

Goleman's model outlines four main EI constructs:

Self-awareness - the ability to read one's emotions and recognize their impact while using gut feelings to guide decisions.

Self-management - involves controlling one's emotions and impulses and adapting to changing circumstances.

Social awareness - the ability to sense, understand, and react to other's emotions while comprehending social networks .

Relationship management - the ability to inspire, influence, and develop others while managing conflict .

Goleman includes a set of emotional competencies within each construct of EI. Emotional competencies are not innate talents, but rather learned capabilities that must be worked on and developed to achieve outstanding performance. Goleman posits that individuals are born with a general emotional intelligence that determines their potential for learning emotional competencies.

The Bar-On model of Emotional-Social Intelligence (ESI)

Psychologist Reuven Bar-On (2006) developed one of the first measures of EI that used the term " Emotion Quotient ". He defines emotional intelligence as being concerned with effectively understanding oneself and others, relating well to people, and adapting to and coping with the immediate surroundings to be more successful in dealing with environmental demands. Bar-On posits that EI develops over time and that it can be improved through training, programming, and therapy.

Bar-On hypothesizes that those individuals with higher than average E.Q.’s are in general more successful in meeting environmental demands and pressures. He also notes that a deficiency in EI can mean a lack of success and the existence of emotional problems. Problems in coping with one’s environment are thought, by Bar-On, to be especially common among those individuals lacking in the subscales of reality testing, problem solving, stress tolerance, and impulse control. In general, Bar-On considers emotional intelligence and cognitive intelligence to contribute equally to a person’s general intelligence , which then offers an indication of one’s potential to succeed in life.

The Trait EI model

Petrides et al. (2000a, 2004, 2007) proposed a conceptual distinction between the ability based model and a trait based model of EI. Trait EI (or ‘trait emotional self-efficacy’) refers to "a constellation of behavioral dispositions and self-perceptions concerning one’s ability to recognize, process, and utilize emotion-laden information". This definition of EI encompasses behavioral dispositions and self perceived abilities and is measured by self report , as opposed to the ability based model which refers to actual abilities as they express themselves in performance based measures. Trait EI should be investigated within a personality framework.

The trait EI model is general and subsumes the Goleman and Bar-On models discussed above. Petrides et al. are major critics of the ability-based model and the MSCEIT arguing that they are based on "psychometrically meaningless" scoring procedures (e.g., Petrides, Furnham, & Mavroveli, 2007).

The conceptualization of EI as a personality trait leads to a construct that lies outside the taxonomy of human cognitive ability. This is an important distinction in as much as it bears directly on the operationalization of the construct and the theories and hypotheses that are formulated about it [17] . The trait EI model is among the most salient in the scientific literature.

topWhat is Mensa ?

Mensa is the largest, oldest, and most famous high-IQ society in the world. The not-for-profit organization restricts its membership to people with high testable IQs. Specifically, potential members must score within the 98th percentile or higher of any approved standardized intelligence test. Mensa is formally composed of national groups and the umbrella organization Mensa International.

Background

Roland Berrill, an Australian barrister, and Dr. Lancelot Ware, a British scientist and lawyer, founded Mensa in the United Kingdom in 1946. They had the idea of forming a society for bright people, the only qualification for membership being a high IQ.

The aims are to create a non-political society free from all social distinctions (racial, religious, etc.). The society welcomes all people, regardless of background, whose IQs meet the criteria, with the objective of members enjoying each other's company and participating in a wide range of social and cultural activities.

Mensa accepts individuals who score at or above the 98th percentile on certain standardized IQ tests, such as the Stanford-Binet. Because different tests are scaled differently, it is not meaningful to compare raw scores between tests, only percentiles. For example, the minimum accepted score on the Stanford-Binet is 132, while for the Cattell it is 148.

In addition to encouraging social interaction among its members, the organization is also involved with programs for gifted children, literacy, and scholarships. The name comes from mensa, the Latin word for "table", and indicates that it is a round-table society of equals (although the logo can be seen as depicting a square table, or Parsons table).

Mensa's goals

Mensa's constitution lists three purposes: to identify and foster human intelligence for the benefit of humanity; to encourage research into the nature, characteristics, and uses of intelligence; and to provide a stimulating intellectual and social environment for its members. Its constitution also states that "Mensa encompasses members representing many points of view. Consequently, Mensa as an organization shall not express an opinion as being that of Mensa, take any political action other than the publication of the results of its investigations, or have any ideological, philosophical, political, or religious affiliations."

Mensa has published a number of books, including Poetry Mensa (1966), an anthology of poems by Mensans from all over the world, in which languages other than English are represented. The Mensa Foundation, a separate charitible U.S. Corporation, edits and publishes its own Mensa Research Journal, in which both Mensans and non-Mensans are published on various topics surrounding the concept and measure of intelligence. The national groups also issue periodicals, such as Mensa Bulletin, the monthly publication of American Mensa, and Mensa Magazine, the monthly publication of British Mensa.

At Mensa's 50th Anniversary, Dr. Ware, one of the founders, addressed Mensans by stating that he hoped that “Mensa will have a role in society when it gets through the ages of infancy and adolescence.” He also said, “I do get disappointed that so many members spend so much time solving puzzles,” expressing his desire for Mensans instead to be solving some of the world's problems.

Organizational structure

Mensa International consists of over 100,000 members in 50 national groups. Individuals who live in a country with a national group join the national group, while those living in countries without a recognised chapter may join Mensa International directly. The two largest national groups are American Mensa, with about 50,000 members, and British Mensa, with about 25,500 members. Larger national groups are further subdivided into local groups. For example, American Mensa has over 135 local groups, with the largest having over 2,000 members and the smallest having fewer than 100.

Additionally, members may form Special Interest Groups (SIGs) at international, national, and local levels; these SIGs represent a wide variety of interests, both commonplace and obscure, ranging from motorcycle clubs to entrepreneurial cooperations, reflecting the wide diversity of members in occupation and social class. Some SIGs are associated with various geographic groups, whereas others act independently of official hierarchy. There are now quite a number of electronic SIGs (eSIGs), which operate primarily as e-mail lists, where members may or may not meet each other in person.

Mensa demographics

Mensans come from all walks of life and almost every job and profession, representing almost every age group. There are many famous and prominent members. Members pay annual membership dues that vary by country; some national groups offer a "Life Membership", but it is not transferable between groups.

All national and local groups welcome children; many offer activities, resources and newsletters specifically geared toward gifted children and their parents. American Mensa, for instance, has 1300 child members, ranging in age from 3 to 18. The youngest person who have joined the organization was aged 2 years and nine months. At the other extreme the oldest member of American Mensa is listed as 102. According to the American Mensa site 41 percent of the membership is between the ages of 44 and 61 and just under 60 percent of the new members in 2004 were between the ages of 23 and 43. There are more than 1,500 families with two or more Mensa members.

topWhat is UberMens ?

UberMens is the largest social network for only highly intelligent. Specifically, potential members must score within the 90th percentile or higher on an approved standardized intelligence test. UberMens exists in the US, Canada, Australia and Germany. In China it operates under the name of GaoZhiShang.

Requirements to enter UberMens

To enter UberMens an applicant must have a recommendation from a friends who is already a member and must pass an IQ test. The IQ test is composed of verbal, mathematical and graphical questions of varying difficulty.

topIs IQ determined by genes or by environment?

Heritability

The role of genes and environment (nature and nurture) in determining IQ is reviewed in Plomin et al. (2001, 2003). Until recently heritability was mostly studied in children. Various studies find the heritability of IQ between 0.4 and 0.8 in the United States ; that is, depending on the study, a little less than half to substantially more than half of the variation in IQ among the children studied was due to variation in their genes. The remainder was thus due to environmental variation and measurement error. A heritability in the range of 0.4 to 0.8 implies that IQ is "substantially" heritable.

The effect of restriction of range on IQ was examined by Matt McGue and colleagues, who write that "restriction in range in parent disinhibitory psychopathology and family SES had no effect on adoptive-sibling correlations ... IQ". On the other hand, a 2003 study by Eric Turkheimer, Andreana Haley, Mary Waldron, Brian D'Onofrio, Irving I. Gottesman demonstrated that the proportions of IQ variance attributable to genes and environment vary with socioeconomic status. They found that in impoverished families, 60% of the variance in IQ is accounted for by the shared environment, and the contribution of genes was close to zero.

It is reasonable to expect that genetic influences on traits like IQ should become less important as one gains experiences with age. Surprisingly, the opposite occurs. Heritability measures in infancy are as low as 20%, around 40% in middle childhood, and as high as 80% in adulthood. The American Psychological Association's 1995 task force on "Intelligence: Knowns and Unknowns" concluded that within the white population the heritability of IQ is "around .75". The Minnesota Study of Twins Reared Apart, a multiyear study of 100 sets of reared-apart twins which was started in 1979, concluded that about 70% of the variance in IQ was found to be associated with genetic variation. Some of the correlation of IQs of twins may be a result of the effect of the maternal environment before birth, shedding some light on why IQ correlation between twins reared apart is so robust.

There are a number of points to consider when interpreting heritability:

A high heritability does not mean that the environment has no effect on the development of a trait, or that learning is not involved. Vocabulary size, for example, is very substantially heritable (and highly correlated with general intelligence) although every word in an individual's vocabulary is learned. In a society in which plenty of words are available in everyone's environment, especially for individuals who are motivated to seek them out, the number of words that individuals actually learn depends to a considerable extent on their genetic predispositions.

A common error is to assume that because something is heritable it is necessarily unchangeable. This is wrong. Heritability does not imply immutability. As previously noted, heritable traits can depend on learning, and they may be subject to other environmental effects as well. The value of heritability can change if the distribution of environments (or genes) in the population is substantially altered. For example, an impoverished or suppressive environment could fail to support the development of a trait, and hence restrict individual variation. Differences in variation of heritability are found between developed and developing nations. This could affect estimates of heritability. Another example is Phenylketonuria which previously caused mental retardation for everyone who had this genetic disorder. Today, this can be prevented by following a modified diet.

On the other hand, there can be effective environmental changes that do not change heritability at all. If the environment relevant to a given trait improves in a way that affects all members of the population equally, the mean value of the trait will rise without any change in its heritability (because the differences among individuals in the population will stay the same). This has evidently happened for height: the heritability of stature is high, but average heights continue to increase.[13]

Even in developed nations, high heritability of a trait within a given group has no necessary implications for the source of a difference between groups.

Environment

Environmental factors play a role in determining IQ. Proper childhood nutrition appears critical for cognitive development ; malnutrition can lower IQ. Other research indicates environmental factors such as prenatal exposure to toxins , duration of breastfeeding , and micronutrient deficiency can affect IQ.

It is well known that it is possible to increase one's IQ score by training, for example by regularly playing puzzle games, or strategy games like Chess . Musical training in childhood also increases IQ. Recent studies have shown that training in using one's working memory may increase IQ.

Family environment

In the developed world, nearly all personality traits show that, contrary to expectations, environmental effects actually cause non-related children raised in the same family ("adoptive siblings") to be as different as children raised in different families. There are some family effects on the IQ of children, accounting for up to a quarter of the variance. However, by adulthood, this correlation disappears, such that adoptive siblings are not more similar in IQ than strangers. For IQ, adoption studies show that, after adolescence, adoptive siblings are no more similar in IQ than strangers (IQ correlation near zero), while full siblings show an IQ correlation of 0.6. Twin studies reinforce this pattern: monozygotic (identical) twins raised separately are highly similar in IQ (0.86), more so than dizygotic (fraternal) twins raised together (0.6) and much more than adoptive siblings (~0.0). The American Psychological Association 's report Intelligence: Knowns and Unknowns (1995) states that there is no doubt that normal child development requires a certain minimum level of responsible care. Severely deprived, neglectful, or abusive environments must have negative effects on a great many aspects of development, including intellectual aspects. Beyond that minimum, however, the role of family experience is in serious dispute. Do differences between children's family environments (within the normal range) produce differences in their intelligence test performance? The problem here is to disentangle causation from correlation. There is no doubt that such variables as resources of the home and parents' use of language are correlated with children's IQ scores, but such correlations may be mediated by genetic as well as (or instead of) environmental factors. But how much of that variance in IQ results from differences between families, as contrasted with the varying experiences of different children in the same family? Recent twin and adoption studies suggest that while the effect of the family environment is substantial in early childhood, it becomes quite small by late adolescence. These findings suggest that differences in the life styles of families whatever their importance may be for many aspects of children's lives make little long-term difference for the skills measured by intelligence tests. It also stated "We should note, however, that low-income and non-white families are poorly represented in existing adoption studies as well as in most twin samples. Thus it is not yet clear whether these studies apply to the population as a whole. It remains possible that, across the full range of income and ethnicity, between-family differences have more lasting consequences for psychometric intelligence."

A study of French children adopted between the ages of 4 and 6 shows the continuing interplay of nature and nurture. The children came from poor backgrounds with IQs that initially averaged 77, putting them near retardation. Nine years later after adoption, they retook the I.Q. tests, and all of them did better. The amount they improved was directly related to the adopting family’s status. "Children adopted by farmers and laborers had average I.Q. scores of 85.5; those placed with middle-class families had average scores of 92. The average I.Q. scores of youngsters placed in well-to-do homes climbed more than 20 points, to 98." On the other hand, the degree to which these increases persisted into adulthood are not clear from the study.