Intelligence & IQ Testing: Concepts, Theories, and Controversies

Intelligence: Definitions and Core Abilities

What is Intelligence?

Intelligence is broadly defined as the ability to learn from experience, solve problems, and use knowledge to adapt to new situations. It is also socially constructed, with cultures valuing different attributes as 'intelligent' based on what enables success in that context.

• Key Abilities:

  • Reason abstractly

  • Adapt to novel environmental circumstances

  • Acquire knowledge

  • Benefit from experience

• Example: Solving a new type of puzzle or adapting to a new job environment.

Origins of Intelligence Testing

Binet & Simon: The First Intelligence Test

The French government commissioned Alfred Binet and Theodore Simon in 1904 to develop the first intelligence test to identify slow and fast learners. Their test predicted children's progress based on mental age.

• Diverse Content: Object naming, drawing pictures, word meanings, incomplete sentences, memory sentence completion.

• Modern intelligence tests still follow Binet and Simon's approach.

Theories of Intelligence

Charles Spearman and General Intelligence (g)

Spearman observed that scores on different intelligence test items were positively correlated, leading to the concept of a single shared factor: general intelligence (g). This factor reflects the overall strength of mental abilities.

• g: Represents overall mental ability; controversial but widely supported.

• s: Specific abilities relevant to particular tasks.

Fluid and Crystallized Intelligence

Modern theories distinguish between two major types of intelligence:

• Fluid Intelligence: The ability to learn new ways of solving problems (e.g., solving a puzzle for the first time).

• Crystallized Intelligence: Accumulated knowledge over time (e.g., knowing the capital of a country).

• Fluid intelligence tends to decline with age, while crystallized intelligence may increase.

• Crystallized intelligence is moderately associated with personality traits like openness to experience.

Multiple Intelligences (Gardner) and Triarchic Theory (Sternberg)

• Gardner's Multiple Intelligences: Proposes several independent intelligences, such as linguistic, logical-mathematical, spatial, bodily-kinesthetic, musical, interpersonal, intrapersonal, and naturalistic.

• Sternberg's Triarchic Theory:

  • Analytical Intelligence: Problem-solving with single correct answers ('book smarts').

  • Creative Intelligence: Adapting to novel situations.

  • Practical Intelligence: Everyday tasks and 'street smarts'.

• Neither model has conclusively shown independence from 'g'.

Biological Correlates of Intelligence

Brain Size and Perceptual Speed

Research shows a moderate correlation (about r = .40) between brain size and intelligence. However, correlation does not imply causation.

• Higher intelligence may be associated with faster perceptual speed and quicker response times.

• Brain size decreases with age, as do scores on non-verbal intelligence tests.

Modern Intelligence Tests

Wechsler Scales

David Wechsler developed the Wechsler Adult Intelligence Scale (WAIS) and the Wechsler Intelligence Scale for Children (WISC). These tests measure various mental abilities and provide an overall IQ score.

• Abilities Measured: Vocabulary, arithmetic, spatial ability, verbal reasoning, general knowledge.

• WAIS-IV: Measures overall intelligence and 15 other aspects.

• Index Scores:

  • Verbal Comprehension Index (VCI)

  • Perceptual Reasoning Index (PRI)

  • Working Memory Index (WMI)

  • Processing Speed Index (PSI)

IQ Scores and Standardization

IQ scores are standardized to fit a normal distribution curve, with a mean of 100 and a standard deviation of 15.

• Formula for IQ: $IQ = \frac{\text{mental age}}{\text{chronological age}} \times 100$

• Scaled scores have a mean of 10 and S.D. of 3.

• Information subtest correlates with full scale IQ at r = .76; test-retest reliability = .94.

Test Construction: Reliability and Validity

Key Concepts

• Reliability: Consistency of test scores over time.

• Validity: Whether a test measures what it is supposed to measure.

• Culture Fair Tests: Designed to minimize cultural and language biases by using abstract reasoning items.

IQ and Real-World Outcomes

Predictive Value of IQ

• IQ scores predict academic success (correlation about .50 with grades).

• IQ predicts performance across a wide variety of careers, but the correlation with job performance is lower (about .15).

• IQ is associated with health-related outcomes, including sickness and car accidents.

• Motivation, curiosity, effort, and perseverance also play crucial roles in success.

Test Bias and Racial Differences

Test Bias

• A test is considered biased if it predicts outcomes better in one group than another, not simply if groups score differently.

• Most research finds that IQ tests predict academic and occupational achievement equally across races.

Racial Differences in IQ

• On average, African and Hispanic Americans score lower than Caucasians on standard IQ tests; Asian Americans score higher than Caucasians.

• Estimated average difference between Caucasians and African Americans can be up to 15 points, but variability within races is much larger than between races.

• Race cannot be used to infer an individual's IQ.

Biological and Environmental Influences on IQ

Biological Determinants

• Some argue that IQ differences are largely genetic (e.g., twin studies show high heritability).

• Identical twins raised apart have more similar IQs than fraternal twins raised together.

Environmental Determinants

• Socioeconomic status, education, and environment play significant roles in IQ differences.

• Poor Whites in the U.S. score 10-20 points lower than middle-class Whites; Black children adopted by White families show higher IQs than average Whites.

• Flynn Effect: IQ scores have risen over generations, suggesting environmental factors are important.

Summary Table: Major Theories and Tests of Intelligence

Theory/Test	Main Features	Key Figures
General Intelligence (g)	Single underlying factor for mental ability	Charles Spearman
Fluid/Crystallized Intelligence	Fluid: novel problem-solving; Crystallized: accumulated knowledge	Cattell, Horn
Multiple Intelligences	Several independent intelligences	Howard Gardner
Triarchic Theory	Analytical, Creative, Practical intelligence	Robert Sternberg
Stanford-Binet Test	First standardized intelligence test	Binet, Simon, Terman
Wechsler Scales (WAIS, WISC)	Measures multiple mental abilities, overall IQ	David Wechsler

Key Equations

• IQ Formula: $IQ = \frac{\text{mental age}}{\text{chronological age}} \times 100$

Additional info:

• Notes include expanded context and examples for clarity and completeness.