Intelligence Tests (College Board AP® Psychology): Revision Note

The Stanford-Binet IQ test

• The first formal intelligence test was developed by Alfred Binet in France to identify children who needed additional support in school

  • Binet introduced the concept of mental age, which is the level of intellectual functioning typical of a child of a given age

    • A child's mental age was compared to their chronological age (their actual age) to produce a score

• Lewis Terman at Stanford University adapted Binet's test for American use and introduced the formula for calculating the intelligence quotient (IQ):

  • IQ = (mental age ÷ chronological age) × 100

    • E.g. a 10-year-old child with a mental age of 10 has an IQ of 100 (10 ÷ 10 × 100); a 10-year-old with a mental age of 12 has an IQ of 120

• The resulting test became known as the Stanford-Binet IQ test

  • This was the first widely used standardized intelligence test

• In modern use, IQ scores are calculated differently, using deviation IQ, which compares a person's score to the average performance of others

• IQ scores follow a normal distribution with a mean of 100 and a standard deviation of 15

  • Approximately 68% of people score between 85 and 115; approximately 95% score between 70 and 130

• In modern times, IQ scores are often used to identify students for educational services

The Wechsler IQ tests

• David Wechsler developed a family of intelligence tests designed to address limitations of the Stanford-Binet:

  • Wechsler Adult Intelligence Scale (WAIS) for adults aged 16 and over

  • Wechsler Intelligence Scale for Children (WISC) for children aged 6–16

  • Wechsler Preschool and Primary Scale of Intelligence (WPPSI) for children aged 2.5–7

• The Wechsler tests differ from the Stanford-Binet in important ways:

  • They yield both an overall IQ score and separate scores for specific subtests, giving a more detailed profile of a person's cognitive strengths and weaknesses

  • Subtests cover six types of questions: information, comprehension, arithmetic, similarities, digit span, and vocabulary

• This reflects Wechsler's view that intelligence involves a combination of abstract and verbal measures rather than a single score

• The Wechsler tests are among the most widely used intelligence assessments in the world today

Psychometric principles: standardization, reliability, and validity

• For any psychological test, such as including intelligence tests, to be considered useful, it must adhere to the following psychometric principles:

  • standardization

  • reliability

  • validity

Standardization

• A test is standardized when it is administered using consistent procedures and environments for all test-takers

  • Standardization ensures that scores are comparable across individuals by ensuring everyone takes the test under the same conditions

• A standardization sample is a large, representative group used to establish the norms against which individual scores are compared

  • E.g. IQ scores are standardized so that a score of 100 always represents average performance for a given age group. This is only meaningful if the test was administered consistently to a representative sample

Reliability

• A test is reliable if it yields similar results each time it is administered to the same person under similar conditions

  • Reliability is measured using a correlation coefficient - a score of 1.0 indicates perfect reliability

• Two types of reliability are required:

  • Test-retest reliability: the same test administered to the same person on two separate occasions should produce similar scores

    • E.g. if you take an IQ test today and again in three months, a reliable test should produce approximately the same score both times

  • Split-half reliability: the test is divided into two halves and scores on each half are correlated. A reliable test should produce similar scores on both halves

• A test can be reliable without being valid, but a valid test must be reliable

Validity

• A test is valid if it measures what it is designed to measure

• Two types of validity are required:

  • Construct validity: the degree to which the test actually measures the theoretical construct it claims to measure

    • E.g. does an IQ test genuinely measure intelligence, or is it measuring something else such as test-taking skill or cultural familiarity?

  • Predictive validity: the degree to which the test score accurately predicts future performance on a relevant outcome

    • E.g. an IQ test has predictive validity if high scorers consistently go on to perform well in academic and professional settings

• A test that is not valid is not useful, regardless of how reliable it is

Systemic issues: stereotype threat, Flynn effect, bias, and historical misuse

• Intelligence testing does not occur in a vacuum

  • Scores are influenced by social, cultural, and historical factors that must be understood to interpret them responsibly

Stereotype threat and stereotype lift

• Stereotype threat occurs when awareness of a negative stereotype about one's group causes a person to perform below their potential on a test

  • The anxiety of possibly confirming the stereotype impairs performance

    • E.g. research has shown that when women are reminded of the stereotype that men perform better at math before a math test, their scores decrease, even though no such difference exists under neutral conditions

• Stereotype lift is the complementary effect

  • Members of a group that is positively stereotyped on a measure may perform better than expected when the stereotype is made salient

• Researchers strive to develop assessments that are socioculturally responsive, i.e. designed to reduce the influence of stereotype threat and cultural bias on scores

The Flynn effect

• The Flynn effect is the finding that IQ scores across much of the world have generally increased over time

  • Average IQ scores have risen by approximately 3 points per decade over the 20th century

• This increase is too rapid to be explained by genetic change, therefore it is attributed to societal factors such as:

  • higher socioeconomic status and improved nutrition

  • better access to healthcare

  • increased access to education and more cognitively stimulating environments

• The Flynn effect demonstrates that IQ scores are not fixed biological measurements, but are significantly influenced by environmental and social conditions

Bias and group differences

• IQ scores tend to vary more within any given group than between groups, meaning the differences between individuals within a group are larger than the average differences between groups

  • This is a critical point as knowing someone's group membership tells you very little about their individual intelligence

• Personal and sociocultural biases can distort the interpretation of individual IQ scores:

  • Poverty, discrimination, and educational inequities have been shown to negatively influence intelligence scores of individuals and groups

• IQ tests have historically been criticized for containing items that reflect the knowledge and experiences of white, middle-class, Western cultures

  • This places test-takers from other backgrounds at a systematic disadvantage

Historical misuse of intelligence tests

• IQ scores have been used historically to limit access to jobs, military ranks, educational institutions, and immigration to the US:

  • During World War I, army intelligence tests were used to rank recruits

    • Results were used to argue for the intellectual inferiority of certain racial and immigrant groups, despite the tests being culturally biased

  • IQ testing was used to justify discriminatory immigration policies in the early 20th century, restricting entry to the US from certain countries on the basis of alleged low intelligence

• These historical uses demonstrate that intelligence tests are not neutral instruments

  • Their design, administration, and interpretation are all shaped by the social and political contexts in which they are used