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Week 6: Intelligence Testing – Comprehensive Notes

Defining Intelligence

  • Intelligence encompasses multiple domains, including abstract reasoning, problem solving, the capacity to acquire new knowledge, memory, adaptability to the environment, mental speed, linguistic competence, general knowledge, and creativity.

  • Definitions across influential theorists emphasize a combination of cognitive capacities that facilitate goal-directed behavior and adaptive functioning.

    • Classic definitions include:

    • Spearman (1904): A general ability to infer relations and correlates.

    • Binet (1916): Tendency to pursue and maintain a definite direction; capacity to adapt to attain a desired end; power of autocriticism.

    • Thurstone (1921): Ability to inhibit instinctive adjustments, think flexibly, imagine different responses, and implement modified adjustments in overt behavior.

    • Wechsler (1939): Aggregate or global capacity to act purposefully, think rationally, and deal effectively with the environment.

    • Sternberg (1985): Mental activities involved in purposive adaptation to, shaping of, and selection of real-world environments relevant to life.

  • IQ and its conceptualization

    • Intelligence quotient (IQ) is a measure that is almost synonymous with intelligence and is widely used by laypeople and academics.

    • IQ scores are typically represented by a normal distribution (bell curve) with a mean of 100 and a standard deviation of 15.

    • The concept of a latent construct underpins much of the psychometric approach to intelligence.

  • Conceptualization of intelligence

    • Intelligence is viewed as a latent construct that can be quantified through standardized performance tests.

    • The psychometric approach treats intelligence as a series of abilities that can be measured by tests and derived from testing data.

Theories of Intelligence

  • Alfred Binet: Intelligence as the combined capacity to maintain a definite direction, adjust as needed to achieve goals, and critically reflect to adapt; components include reasoning, judgment, memory, and abstraction; general mental ability arises from interactions of abilities; intelligence increases with age in children.

  • Charles Spearman: g (general mental ability) underlies performance across diverse abilities; intelligence comprises a single general factor (g) plus specific factors (s).

  • Lewis Thurstone: Rather than a single general factor, there are several broad group factors (primary abilities); proposed seven primary abilities and emphasized adaptive, goal-oriented processing.

  • David Wechsler: Intelligence as a global capacity but influenced by non-intellective factors (affective traits, motivation, persistence); assesses multiple differential abilities to form a full index (e.g., verbal and non-verbal domains).

  • Robert Sternberg: Triarchic theory of intelligence combining analytical, creative, and practical aspects; successful performance depends on identifying strengths, compensating for weaknesses, and adapting to, shaping, and selecting environments; intelligence is malleable.

  • Jean Piaget: Intellectual development results from the interaction of biological factors and environment; progression through assimilation and accommodation; four major development stages: sensorimotor, preoperational, concrete, and formal operational.

  • Cattell–Horn–Carroll (CHC) model (advancement referenced): Integrates fluid intelligence (Gf), crystallized intelligence (Gc), and other broad and narrow abilities into a hierarchical framework; CHC aided the understanding of intelligence as a structured system of cognitive abilities.

Intelligence Quotient (IQ) and Conceptualization

  • IQ as a central concept in intelligence testing is closely tied to a normal distribution with a mean of 100 and an SD of 15.

  • Conceptualizing intelligence as a latent construct supports a psychometric approach in which cognitive abilities are inferred from performance on standardized tests.

  • Two key formulations of IQ measurement appear in the history of testing:

    • Mental Age (MA) and Chronological Age (CA) approach:

    • Stanford-Binet initially used MA/CA to derive IQ; later versions refined this into deviation-based scoring.

    • Deviation IQ: A standard score with a mean of 100 and SD of 15, designed to keep IQ scores comparable across ages.

  • Theoretical implications

    • Intelligence is often treated as a spectrum of abilities that can be measured, compared, and interpreted through standardized testing.

    • Practical implications include educational placement, clinical assessment, and research on cognitive development and aging.

Part 1–5 Overview (Lecture Structure)

  • Part 1: Defining intelligence

  • Part 2: Theories of intelligence

  • Part 3: Nature vs Nurture

  • Part 4: Measurement of intelligence

  • Part 5: Lifespan trends in intelligence

Nature vs Nurture: Foundations

  • Early views emphasized heredity (nature) as the primary determinant of intelligence, sparking debate about environmental influence.

  • Francis Galton (late 19th century) argued that nature dominates, attributing strong genetic influence to intelligence.

  • Contemporary research emphasizes both genes and environment, with interplay between biological and environmental factors.

  • Research designs used to study nature–nurture effects include family studies, adoption studies, and twin studies (monozygotic/MZ and dizygotic/DZ) to separate genetic and environmental influences.

  • Visual depiction (described):

    • Family studies compare genetic relatedness and shared environments across relatives.

    • Adoption studies distinguish genetic influences from rearing environments by separating genetic and adoptive parents.

    • Twin studies compare concordance rates in MZ vs DZ twins to estimate genetic contribution and environmental effects.

  • Key findings from recent studies:

    • Heritability estimates for intelligence tend to increase with age, from around 20% in infancy to perhaps 80% in adulthood.

    • Shared environmental influences can significantly moderate non-shared environmental effects on academic achievement and verbal intelligence.

    • Intelligence is closely associated with education and social class.

  • Interplay between environment and genes involves several environmental factors that can influence cognitive development: diet, toxins, education, poverty and resource availability, environmental stimulation, motivation and expectancy.

  • Interplay takeaway: Genetic relatedness correlates with IQ, and shared environments positively predict IQ, though genetic effects are substantial; twin studies suggest that a sizable portion of variance is attributable to environmental influences, particularly earlier in development.

  • Controversy example (academic debate): A 2009 Nature article presented opposing views

    • Steven Rose argued against studying race and IQ from a scientific standpoint, claiming potential harms and misinterpretations.

    • Ceci & Williams argued for pursuing scientific inquiry into race and IQ to advance understanding, with the view that scientific truth should be pursued.

Measurement of Intelligence

  • The Binet scales

    • 1904: Alfred Binet commissioned to identify children with limited intellectual ability; 1905 version introduced.

    • 1908 version grouped items by age; introduced the concept of mental age (MA) vs chronological age (CA): a child performing at the level of an older peer has a higher MA.

  • The Stanford-Binet (SB) scales

    • SB-1 (1916): Introduced the intelligence quotient (IQ) score: IQ = rac{MA}{CA} imes 100

    • SB-3 (1960): Introduced deviation IQ with mean 100 and SD 16 (later standardization used SD 15).

    • Modern Binet scales (SB-5, 2003): Built on a three-level hierarchical model aligned with CHC; emphasizes a contemporary framework for cognitive abilities.

  • Wechsler scales overview

    • Wechsler proposed intelligence as a global capacity but with emphasis on both cognitive abilities and non-intellective factors (affective traits, motivation, persistence).

    • Wechsler scales measure multiple facets of intelligence across verbal and nonverbal domains, including processing speed and working memory.

  • Wechsler Adult Intelligence Scale (WAIS) family

    • WAIS, WAIS-R, WAIS-III and WAIS-IV have been developed; WAIS-IV (2008) norms updated to reflect the Flynn effect.

    • WAIS scales are based on a deviation IQ framework (mean 100, SD 15).

    • Subscales are organized into index composites and provide a Full Scale IQ (FSIQ) and a General Ability Index (GAI).

  • Wechsler indices (WAIS-IV)

    • Verbal Comprehension Index (VCI): Verbal knowledge and verbal reasoning; requires understanding of words and social knowledge.

    • Working Memory Index (WMI): Ability to retain and manipulate information in working memory; supports arithmetic, attention, and problem solving.

    • Perceptual Reasoning Index (PRI): Visual perception and organization; nonverbal reasoning, fluid reasoning.

    • Processing Speed Index (PSI): Visual processing speed, attention, and motor speed.

    • General Ability Index (GAI): Derived from six subtests combining Verbal Comprehension and Perceptual Reasoning to estimate cognitive ability independent of working memory and processing speed.

  • WAIS-IV core subtests and structure

    • Core subtests (examples shown in the slides):

    • Vocabulary, Similarities, Information, Comprehension, Arithmetic, Digit Span, Letter-Number Sequencing, Block Design, Matrix Reasoning, Visual Puzzles, Figure Weights, Digit Symbol-Coding, Symbol Search, Cancellation.

    • Core index assignments map to the four WAIS-IV indices: VCI, WMI, PRI, PSI; with VIQ and PIQ aligning to Verbal and Performance manifestations.

    • Norms: WAIS-IV standardization sample of approximately 2,200 individuals aged 16–90 in the United States; culture bias remains a consideration when applying norms cross-culturally.

  • SB-5 features (2003) and measurement implications

    • SB-5 sits on a three-level hierarchical CHC-based model of intelligence.

    • Uses a hybrid of point and age-based scoring; balance of verbal and non-verbal items; routing tests help determine the starting level (ability to begin testing at an appropriate level).

    • Basal and ceiling rules regulate the testing process; basal = minimum criterion of correct responses from the start point; ceiling = number of incorrect responses that terminates testing.

    • Uses SD of 15 for IQ and factor scores.

    • Demonstrates psychometric robustness and cross-age applicability.

  • Non-intellective factors

    • Wechsler emphasized the role of affective and personality traits, such as emotional awareness, frustration tolerance, drive to excel, persistence, and goal awareness, in contributing to observed performance.

Measurement of Intelligence: Indexes and Subtests (WAIS-IV specifics)

  • Verbal Comprehension Index (VCI): Assesses verbally acquired knowledge and verbal reasoning; includes measures of stored knowledge, oral expression, general verbal skills; requires understanding of words and social knowledge.

  • Working Memory Index (WMI): Assesses the ability to temporarily retain information in memory and manipulate it; includes arithmetic skills and problem solving; requires sustained attention and reasoning.

  • Perceptual Reasoning Index (PRI): Assesses visual perception, organization, and nonverbal reasoning; includes fluid reasoning and comfort with new or unexpected situations.

  • Processing Speed Index (PSI): Assesses quick processing of visual information; includes attention, processing speed, fine motor coordination.

  • Sample core subtests (illustrative):

    • Vocabulary, Similarities, Information, Comprehension, Arithmetic, Digit Span, Letter-Number Sequencing, Block Design, Matrix Reasoning, Visual Puzzles, Figure Weights, Digit Symbol-Coding, Symbol Search, Cancellation.

  • WAIS-IV interpretation conventions

    • FSIQ (Full-Scale IQ): Global measure of overall cognitive ability; mean = 100, SD = 15.

    • VIQ (Verbal IQ) and PIQ (Performance IQ): Subcomponent measures of verbal and nonverbal abilities, respectively.

    • GAI (General Ability Index): Composite derived from six subtests that emphasize verbal comprehension and perceptual reasoning, intended to capture general cognitive ability with less influence from working memory and processing speed.

  • Norms and cross-cultural considerations

    • WAIS-IV norms were developed from a representative US sample; cross-cultural validity requires careful interpretation due to potential cultural biases and educational differences.

    • The Flynn effect (rising IQ scores over time) has prompted norm revisions to maintain interpretability of standard scores across cohorts.

The Wechsler Scales and Modern Measurement Practices

  • The WAIS family emphasizes a shift from purely age-based scoring to deviation IQs, which allows scores to be compared across age groups.

  • The WAIS-IV includes 10 core subtests and 5 supplementary subtests, with a total of 14 subtests commonly referenced in clinical and educational settings.

  • The Wechsler approach foregrounds the integration of multiple cognitive domains to form a comprehensive cognitive profile that informs diagnostic and educational decisions.

Lifespan Trends in Intelligence

  • Crystallized intelligence vs fluid intelligence

    • Crystallized intelligence: accumulated knowledge and verbal skills that tend to increase with age.

    • Fluid intelligence: the capacity to reason abstractly and solve novel problems, which tends to decline with age from middle adulthood onward.

  • Cross-sectional vs longitudinal changes

    • Cross-sectional analyses compare individuals of different ages at one point in time, potentially conflating aging effects with cohort effects.

    • Longitudinal analyses follow the same individuals over time to track true age-related changes but are resource-intensive and subject to practice effects and attrition.

  • The Seattle Longitudinal Study (SLS)

    • A cohort-sequential longitudinal study beginning in 1956 with 200 participants in their 20s to late 60s; reassessed in 7-year intervals; later involving 6,000+ participants.

    • The SLS tracked changes in six intellectual abilities over time, providing insights into how different cognitive domains age.

  • The Flynn effect

    • A general trend of increasing IQ scores over time, estimated at roughly
      ext{Flynn effect} \approx 3 \, ext{IQ points per decade}

    • There is broad agreement that this effect exists, but there is no consensus on the precise causes.

  • Explanations for the Flynn effect

    • Increased levels of education and access to educational opportunities across populations.

    • Improvements in nutrition, health, and reductions in infectious diseases.

    • Greater familiarity with IQ-type testing and changes in test-taking motivation and effort.

    • Changes in measurement practices and test content across periods, and environmental factors that shape cognitive development (stimulating environments, job demands, etc.).

  • Crystallized vs Fluid changes across the lifespan: empirical patterns suggest crystallized abilities tend to increase or remain stable, while fluid abilities tend to decline with age, particularly after middle adulthood.

Nature, Nurture, and Practical Implications

  • The evidence base supports a dual influence of genes and environment on intelligence.

  • Practical implications include educational policy, early intervention, and resources aimed at improving environmental conditions (nutrition, education quality, cognitive stimulation).

  • Ethical considerations include how to apply intelligence testing information responsibly in education and social contexts, and how to address concerns about stigmatization and equity.

Summary of Key Formulas and Numerical References

  • IQ formula (early SB approach):
    IQ = \frac{MA}{CA} \times 100

  • Deviation IQ (modern standard):

    • Mean = \mu = 100, Standard Deviation = \sigma = 15

  • General intelligence framework

    • g = \text{general mental ability}

    • Gf (fluid intelligence) and Gc (crystallized intelligence) as key components in CHC theory

  • Flynn effect

    • \Delta IQ \approx 3 \, \, \text{points per decade}

References to Foundational Readings (as per prescribed materials)

  • Shum et al. (2017), Chapter 7 (pp. 132–139; 142–145) and Chapter 9 (pp. 197–203)

  • Additional readings: Articles available on Moodle

Practical Takeaways for Examinations

  • Be able to describe major historical theories of intelligence and their key proponents.

  • Distinguish between web of intelligence constructs (g, Gf, Gc) and the modern CHC model.

  • Explain how IQ is conceptualized and measured, including the difference between MA/CA-derived IQ and deviation IQ.

  • Identify primary measurement tools (SB and WAIS-IV), their structure, core subtests, and what each index assesses.

  • Understand the differences between crystallized and fluid intelligence and how age affects each.

  • Articulate the nature–nurture debate, evidence from family/adoption/twin studies, and contemporary findings on heritability and environmental influences.

  • Recognize the Flynn effect and be able to discuss plausible explanations.

  • Be aware of ethical considerations and contemporary debates (e.g., Race and IQ discussions and differing viewpoints).