Individual Differences 2

A Little History

  1. Charles Spearman:

    • Introduced the concept of general intelligence (g) through factor analysis.

    • Observed a "positive manifold" where performance on various cognitive tasks correlates, suggesting a common underlying factor (g).

  2. Alfred Binet:

    • Developed the first practical intelligence test to identify children needing educational support.

    • Introduced the concept of mental age and the Intelligence Quotient (IQ) formula:

      IQ=(Mental AgeChronological Age)×100IQ=(Chronological AgeMental Age​)×100

    • Binet's test focused on practical skills like naming objects, counting, and identifying body parts.

  3. David Wechsler:

    • Created the Wechsler Adult Intelligence Scale (WAIS), which included both verbal and performance (non-verbal) subtests.

    • The WAIS-IV (2008) is the most widely used IQ test today.

The WAIS (Wechsler Adult Intelligence Scale)

The WAIS measures intelligence across four key indices:

  1. Verbal Comprehension:

    • Vocabulary: Define words.

    • Similarities: Identify how two objects or concepts are alike.

    • Information: Answer general knowledge questions.

  2. Perceptual Reasoning:

    • Block Design: Arrange blocks to match a pattern.

    • Matrix Reasoning: Complete visual patterns.

    • Visual Puzzles: Solve visual-spatial problems.

  3. Working Memory:

    • Arithmetic: Solve math problems.

    • Digit Span: Repeat sequences of numbers (forward and backward).

  4. Processing Speed:

    • Digit-Symbol Coding: Match symbols to numbers quickly.

    • Symbol Search: Identify target symbols within a set.

The Distribution of IQ Scores

  • IQ scores are normally distributed with a mean of 100 and a standard deviation of 15.

  • Giftedness: IQ > 130 (top 2.3% of the population).

  • Intellectual Disability: IQ < 70 (bottom 2.3% of the population).

Reliability and Stability of IQ Scores

  • Reliability: The WAIS-IV has high reliability:

    • Split-half reliability: .97 (consistency within the test).

    • Test-retest reliability: .90 over one year.

  • Stability: IQ scores are highly stable over time:

    • IQ at age 10 correlates ~.70 with IQ at age 40.

    • IQ at age 11 correlates ~.73 with IQ at age 80 (Scottish Mental Survey, 1932).

Validity of IQ Scores

IQ scores predict a wide range of outcomes:

  1. Educational Attainment: Higher IQ increases the likelihood of obtaining a college degree.

  2. Occupational Success: IQ correlates with job performance and income.

  3. Social Outcomes: IQ predicts health, longevity, and even spouse’s IQ.

  4. Negative Correlations: Lower IQ is associated with higher rates of alcoholism, smoking, and accident proneness.

Environmental Effects on IQ

  1. Neurotoxins: Exposure to substances like alcohol (antenatal) and lead (postnatal) can lower IQ.

  2. Nutrition: Better nutrition and breastfeeding are linked to higher IQ.

  3. Education: Early enrichment programs (e.g., Head Start) and schooling increase IQ.

  4. Rearing Environment: Adoption into higher SES families can significantly boost IQ.

  5. Flynn Effect: IQ scores have risen ~3 points per decade in industrialized countries, likely due to improved nutrition, education, and environmental complexity.

Group Differences in IQ

  1. Gender Differences:

    • Mean IQ: No significant difference between men and women.

    • Variability: Men show greater variability in IQ scores.

    • Specific Abilities:

      • Women excel in verbal tasks (e.g., spelling, writing) and arithmetic during childhood.

      • Men excel in spatial tasks (e.g., mental rotation) and complex mathematical reasoning after adolescence.

  2. Racial Differences:

    • Small but statistically significant differences exist (Asian > White > Hispanic > Black).

    • Environmental Factors: Neurotoxins, nutrition, education, and stereotype threat may contribute to these differences.

    • Within-Group Variability: Differences within racial groups are larger than differences between groups.

Beyond g (General Intelligence)

  1. Creativity: Involves divergent thinking (generating multiple solutions) and convergent thinking(finding the best solution).

  2. Interest and Intellect: Our strengths and weaknesses shape our interests and career choices.

  3. Emotional Intelligence: The ability to understand and manage emotions, both our own and others'.

  4. Wisdom: Applying intelligence for the common good.

Ideological Immunity

  • IQ does not protect against belief in pseudoscience, conspiracy theories, or paranormal phenomena.

  • High-IQ individuals may be better at defending their beliefs, even when evidence contradicts them.