Intelligence testing began in an organized way in the early 20th Century with the Stanford-Binet test. The purpose was to form an estimate of a person's aptitude before investing time and money in their education, in the belief that aptitude or intelligence was a fixed quantity.
At the time these tests were developed, medical science and psychology were in their infancy. Ideas such as eugenics still had currency, and intelligence tests were used to weed out so-called "defectives".
Testers classified people as idiots, imbeciles, morons, normal, above average, and geniuses on a numerical scale based on mental age. For children, dividing the mental age by chronological age produces the intelligence quotient (IQ) used for placement in slow or rapid classes.
The study based on survey data from 702 Nordic research works concludes that a typical neuropsychologist used 9 tests in a standard assessment, and 25 tests overall in their practice. The selection of tests to use has been influenced by nationality, competence level, practice profile, and by attitude toward test selection. Testing patients with psychiatric disorders was associated with more tests.[3] The average IQ scores for many populations have been rising at an average rate of three points per decade since the early 20th century (Flynn effect). It is not clear if whether "people are getting more and more clever" or just there are differences between past and current testing.[4][5]
In the United States, intelligence tests were to classify recruits and draftees for service in World War II. The more technical jobs were assigned to men with higher scores. Sociologists also noted racial differences in IQ scores, and some supposed that these differences were inherent. A controversy over this matter has raged ever since.
Open questions for psychologists and sociologists focus on what produces differences in intelligence, whether intelligence can be developed or stunted by upbringing and education, and why different races or cultural groups have significantly different scores.
The two main reasons given are:
After nearly a century of IQ testing and educational reforms, some researchers have begun to assert that IQ can be influenced by the child's environment by as much as 30 points.[6] See Educational games.
A 1976-year study that covered 258 children (IQ between 80 and 119) finally concluded that the major correlating factor is "a favorable parental social and educational background".[7] The more recent 2016-year study also showed that the measured IQ potential is significantly lower in developing countries.[8] and increases after the national statistics improves ([8] references Nigeria and Kenya).
Test results can also be influenced by other factors. Steele and Joshua Aronson found that when they gave a group of Stanford undergraduates a standardized test and told them that it was a measure of their intellectual ability, the white students did much better than their black counterparts. But when the same test was presented simply as an abstract laboratory tool, with no relevance to ability, the scores of blacks and whites were virtually identical.[9] See Pressure and failure.
Socioeconomic factors can cause differences in regional intelligence levels (for example, wealth which can affect the quality of education, health care and nutrition). Although social scientists have disputes about the accuracy of IQ scores in a given region, regions do vary in terms of their IQ scores.[1][10][11] Ethnic groups facing discrimination as immigrants and their IQs temporarily dropping and then later rebounding when the discrimination is over, strongly suggests that IQ is significantly affected by one's environment and not due to any inherent and permanent genetic differences between races.[12]
See also: Genius
A genius is a person who is exceptionally intelligent and/or creative, either generally or in some particular aspect. In terms of general intelligence, a genius or near-genius IQ is considered to start around 140 to 145.[13]
The field of intelligence testing has been acrimonious and contentious. Researchers such as Arthur Jensen and Charles Murray have been pilloried in the mass media, accused of maintaining views which different or even opposite of their actual views.[14]
One professor had to come to Jensen's defense, after Stephen Jay Gould attacked him in print:
Charles Murray said:
The Bell Curve book is not the only controversial study on IQ among different races or groups of people. Danish professor Helmuth Nyborg has conducted studies of IQ which indicate politically incorrect results such as: on average, white people have higher IQs than black people, and men have slightly higher IQs than women. His latest research finds that on average, atheists have IQs about 5.8 points higher than people of faith, prompting similar outrage among his critics, who claim that such results might be due to cultural biases.[7]