13.3: Measuring Intelligence

The goal of most intelligence tests is to measure “G”, the general intelligence factor. Good intelligence tests are reliable, meaning that they are consistent over time, and also demonstrate validity, meaning that they actually measure intelligence rather than something else. Because intelligence is such an important part of individual differences, psychologists have invested substantial effort in creating and improving measures of intelligence, and these tests are now considered the most accurate of all psychological tests.

Intelligence changes with age. A 3-year-old who could accurately multiply 183 by 39 would certainly be intelligent, but a 25-year-old who could not do so would be seen as unintelligent. Thus understanding intelligence requires that we know the norms or standards in a given population of people at a given age. The standardization of a test involves giving it to a large number of people at different ages and computing the average score on the test at each age level.

Once the standardization has been accomplished, we have a picture of the average abilities of people at different ages and can calculate a person’s mental age, which is the age at which a person is performing intellectually. If we compare the mental age of a person to the person’s chronological age, the result is the Intelligence Quotient (IQ), a measure of intelligence that is adjusted for age. A simple way to calculate IQ is by using the following formula:

\[IQ = mental \; age \div chronological \; age \times 100 \]

Thus a 10-year-old child who does as well as the average 10-year-old child has an IQ of 100 (10 ÷ 10 × 100), whereas an 8-year-old child who does as well as the average 10-year-old child would have an IQ of 125 (10 ÷ 8 × 100). Most modern intelligence tests are based on the relative position of a person’s score among people of the same age, rather than on the basis of this formula, but the idea of intelligence “ratio” or “quotient” provides a good description of the score’s meaning.

The Flynn Effect

It is important that intelligence tests be standardized on a regular basis, because the overall level of intelligence (as measured by tests like the Wechsler scales) in a population may change over time. The Flynn effect refers to the observation that scores on intelligence tests worldwide have increased substantially over the past decades (Flynn, 1999). Although the increase varies somewhat from country to country, the average increase is about 3 IQ points every 10 years. There are many explanations for the Flynn effect, including better nutrition, increased access to information, and more familiarity with multiple-choice tests (Neisser, 1998). But whether people are actually getting smarter is debatable (Neisser,1997). [1]

The Value of IQ Testing

The value of IQ testing is most evident in educational or clinical settings. Children who seem to be experiencing learning difficulties or severe behavioral problems can be tested to ascertain whether the child’s difficulties can be partly attributed to an IQ score that is significantly different from the mean for her age group. Without IQ testing—or another measure of intelligence—children and adults needing extra support might not be identified effectively. People also use IQ testing results to seek disability benefits from the Social Security Administration. Some believe in the value of this test as important to help those in need.[2]

However a perusal of the history of IQ theory and testing shows that there have been many vile uses of these tests. At the extreme, IQ tests have sometimes been used as arguments in support of insidious purposes, such as the eugenics movement, which was the science of improving a human population by controlled breeding to increase desirable heritable characteristics. At a seemingly less horrendous, but nonetheless pervasive and macro level, the use of intelligence tests and IQ in particular is highly culturally biased (for example, Shuttleworth-Edwards et al, 2010; Naglieri, 2008; Hessels & Hamers, 1992; Ford, 2008) and has become a tool in systemically marginalizing non-White, non-Eurocentric, and non-individualistic perspectives.

Today, as noted above, IQ tests are used quite regularly and often in educational settings. They are also widely used in neuropsychological assessments, as clinical diagnostic tools (Jewsbury et al, 2016).

Alfred Binet & Théodore Simon - Stanford- Binet Intelligence Test

From 1904- 1905 the French psychologist Alfred Binet (1857–1914) and his colleague Théodore Simon (1872–1961) began working on behalf of the French government to develop a measure that would identify children who would not be successful with the regular school curriculum. The goal was to help teachers better educate these students (Aiken, 1994). It is important to note that Binet was concerned about how his test might be used to discriminate against people.

Binet and Simon developed what most psychologists today regard as the first intelligence test, which consisted of a wide variety of questions that included the ability to name objects, define words, draw pictures, complete sentences, compare items, and construct sentences. Binet and Simon (Binet, Simon, & Town, 1915; Siegler, 1992) believed that the questions they asked the children all assessed the basic abilities to understand, reason, and make judgments.

Figure \(\PageIndex{1}\): (a) Alfred Binet (b) This page is from a 1908 version of the Binet-Simon, Intelligence Scale. Children being tested were asked which face, of each pair, was prettier.[3]

Soon after Binet and Simon introduced their test, the American psychologist Lewis Terman at Stanford University (1877–1956) developed an American version of Binet’s test that became known as the Stanford- Binet Intelligence Test. The Stanford-Binet is a measure of general intelligence made up of a wide variety of tasks including vocabulary, memory for pictures, naming of familiar objects, repeating sentences, and following commands.[4]

David Wechsler- Wechsler-Bellevue Intelligence Scale

In 1939, David Wechsler, a psychologist who spent part of his career working with World War I veterans, developed a new IQ test in the United States. Wechsler combined several subtests from other intelligence tests used between 1880 and World War I. These subtests tapped into a variety of verbal and nonverbal skills, because Wechsler believed that intelligence encompassed “the global capacity of a person to act purposefully, to think rationally, and to deal effectively with his environment” (Wechsler, 1958, p. 7). He named the test the Wechsler-Bellevue Intelligence Scale (Wechsler, 1981). This combination of subtests became one of the most extensively used intelligence tests in the history of psychology.

Figure \(\PageIndex{2}\): David Wechsler[5]

Today, there are three intelligence tests credited to Wechsler, the Wechsler Adult Intelligence Scale-fourth edition (WAIS-IV), the Wechsler Intelligence Scale for Children (WISC-V), and the Wechsler Preschool and Primary Scale of Intelligence—Revised (WPPSI-III) (Wechsler, 2002). These tests are used widely in schools and communities throughout the United States, and they are periodically normed and standardized as a means of recalibration.

Bias of IQ Testing

Intelligence tests and psychological definitions of intelligence have been heavily criticized since the 1970s for being biased in favor of Anglo-American, middle-class respondents and for being inadequate tools for measuring non-academic types of intelligence or talent. Intelligence changes with experience, and intelligence quotients or scores do not reflect that ability to change. What is considered smart varies culturally as well, and most intelligence tests do not take this variation into account. For example, in the West, being smart is associated with being quick. A person who answers a question the fastest is seen as the smartest, but in some cultures being smart is associated with considering an idea thoroughly before giving an answer. A well- thought out, contemplative answer is the best answer.[6]

Sternberg's (2021) more recent ideas about adaptive intelligence as an alternative to G provide some interesting alternative about how intelligence needs to be considered within a context rather than as mental energy.

References:

Ford, D. Y. (2008). Intelligence testing and cultural diversity: The need for alternative instruments, policies and procedures. In VanTassel-Baska J. (Ed.) Alternative Assessments With Gifted and Talented Students. Routledge: New York, NY.

Hessels, M. G. P. & Hamers, J. H. M. (1992). Learning potentials test for ethnic minorities. In Hamers, J.H.M., Ruijssenaars, A.J.J.M., & Sijtsma, K. (Eds.). (1992). Learning Potential Assessment (1st ed.). Taylor & Francis.

Jewsbury, P. A., Bowden, S. C. & Duff, K. (2017). The Cattell–Horn–Carroll Model of cognition for clinical assessment. Journal of Psychoeducational Assessment, 35(6), 547–567. https://doi.org/10.1177/0734282916651360

Naglieri, J.A. (2008). Traditional IQ: 100 Years of Misconception and Its Relationship to Minority Representation in Gifted Programs In VanTassel-Baska J. (Ed.) Alternative Assessments With Gifted and Talented Students. Routledge: New York, NY.

Shuttleworth-Edwards, A. B., Kemp, R. D., Rust, A. L., Muirhead, J. G. L., Hartman, N. P., & Radloff, S. E. (2004) Cross-cultural effects on IQ test performance: A review and preliminary normative indications on WAIS-III test performance, Journal of Clinical and Experimental Neuropsychology, 26()7, 903-920. doi: 10.1080/13803390490510824

Attributions:

Child Growth and Development by Jennifer Paris, Antoinette Ricardo, and Dawn Rymond, 2019, is licensed under CC BY 4.0

[1] Introduction to Psychology - Measures of Intelligence references Psychology by OpenStax CNX, licensed under CC BY 4.0 (modified by Dawn Rymond)

[2] Introduction to Psychology - Measures of Intelligence references Psychology by OpenStax CNX, licensed under CC BY 4.0 (modified by Dawn Rymond)

[3] Images are in the public domain

[4] Introduction to Psychology - Measures of Intelligence references Psychology by OpenStax CNX, licensed under CC BY 4.0

[5] Image by Comet Photo AG (Zürich) is licensed under CC BY-SA 4.0

[6] Sociology: Brief Edition – Agents of Socialization by Steven E. Barkan is licensed under CC BY-NC-SA 3.0

Introduction to Psychology - Measures of Intelligence references Psychology by OpenStax CNX, licensed under CC BY 4.0