Intelligence Testing: Measurement, Types, and Influences

Intelligence Testing

Measuring Intelligence

Intelligence testing is a central topic in psychology, focusing on how cognitive abilities are quantified and interpreted. Psychologists use standardized tests to assess intellectual functioning, but the concept and measurement of intelligence are complex and multifaceted.

• Intelligence as a Construct: In psychological science, intelligence is considered a construct—an abstract concept inferred from observable behavior. Constructs are operationalized for measurement, but their interpretation can have significant social consequences (e.g., eugenics policies).

• Approaches to Testing:

  • Anthropometric Approach (Galton): Early methods focused on measuring physical and sensory variation.

  • Stanford-Binet Test: Assesses ability to think, understand, reason, and adapt. Includes tasks of varying difficulty to determine mental age and IQ (Intelligence Quotient).

  • Deviation IQ: IQ scores are standardized so that the average is 100, with scores distributed normally ($\mu = 100$, $\sigma = 15$).

  • Wechsler Adult Intelligence Scale (WAIS): Measures general ability (GAI) and cognitive proficiency (CPI) through subtests such as verbal comprehension, perceptual reasoning, working memory, and processing speed.

• Problems with Testing:

  • Bias: Language and cultural bias can affect test validity (e.g., Rey Complex Figure test).

  • Eugenics and Racial Superiority: Historical misuse of intelligence testing to justify discrimination.

  • Stereotype Threat: Anxiety about confirming negative stereotypes can impair test performance.

  • Test Validity: Questions about whether tests measure intelligence itself or test-taking skills.

Example: The normal distribution of IQ scores means that most people score near the average, with fewer individuals at the extremes.

Types of Intelligence

Intelligence as a Single Ability

Early theories proposed that intelligence is a general ability underlying all cognitive tasks.

• Spearman's g: The general intelligence factor (g) represents "mental energy" and is correlated with performance across diverse domains (school, work, neural processing).

Intelligence as Multiple Abilities

Contemporary theories recognize that intelligence is multifaceted, consisting of several distinct abilities.

• Spearman's Two-Factor Theory: Intelligence consists of g (general) and s (specific skill-based intelligence).

• Thurstone's Seven Factors: Includes word fluency, verbal comprehension, numeric ability, spatial visualization, memory, perceptual speed, and reasoning.

• Hierarchical Models: General intelligence at the top, with broad and narrow abilities below.

• Fluid vs. Crystallized Intelligence (Cattell):

  • Fluid Intelligence (Gf): Ability to solve novel problems, independent of acquired knowledge.

  • Crystallized Intelligence (Gc): Knowledge and skills acquired through experience and education.

• Gardner's Theory of Multiple Intelligences: Proposes distinct types such as linguistic, logical-mathematical, spatial, musical, bodily-kinesthetic, interpersonal, intrapersonal, naturalist, and existential intelligence.

Example: Raven's Progressive Matrices test fluid intelligence by requiring pattern recognition and logical reasoning.

Do People Have Individualized Learning Styles?

The concept of individualized learning styles (visual, auditory, kinesthetic) is popular but not strongly supported by research. Encoding style and interest are more important than sensory modality.

• Key Point: There is little evidence that teaching to a preferred sensory modality improves learning outcomes.

Influences on Intelligence

Biological Factors

Genetic and biological factors play a significant role in individual differences in intelligence.

• Heritability: The proportion of variance in intelligence attributable to genetic differences. Twin and family studies show substantial heritability.

• Behavioural Genomics: Examines how specific genes influence cognitive abilities.

• Gene Knockout Studies: Experimental removal of genes in animals to study effects on learning and memory.

Example: Monozygotic twins reared apart show more similar IQs than dizygotic twins reared together, indicating genetic influence.

Environmental Factors

Environmental influences are also critical in shaping intelligence.

• Birth Order: Some evidence suggests first-born children may have slightly higher IQs.

• Socioeconomic Status: Access to resources, nutrition, and stimulation affects cognitive development.

• Nutrition: Adequate nutrition is essential for brain development.

• Nootropics: Substances that may enhance cognitive function.

• Education: Schooling and intellectual engagement promote cognitive growth.

Example: Children who stay in school longer tend to have higher IQ scores, highlighting the impact of education.

Table: Comparison of Intelligence Theories

Theory	Main Features	Key Proponents
General Intelligence (g)	Single underlying factor; correlates with performance across domains	Spearman
Multiple Intelligences	Distinct types of intelligence (e.g., linguistic, spatial, musical)	Gardner
Fluid & Crystallized Intelligence	Fluid: problem-solving; Crystallized: acquired knowledge	Cattell
Thurstone's Primary Mental Abilities	Seven independent factors	Thurstone

Key Equations

• IQ Calculation (Stanford-Binet): $\text{IQ} = \frac{\text{Mental Age}}{\text{Chronological Age}} \times 100$

• Deviation IQ: $\text{IQ} = \frac{\text{Individual Score} - \mu}{\sigma} \times 15 + 100$

Additional info: Historical misuse of intelligence testing, such as eugenics policies, highlights the importance of ethical considerations in psychological assessment.