7.5 - measures of intelligence

Intelligence Testing: Development, History, Purposes, and Benefits

1. What is IQ?

• IQ (Intelligence Quotient): A score from standardized tests designed to measure intelligence, traditionally reflecting a person’s cognitive abilities relative to age peers.

• IQ scores are intended to quantify intelligence but involve ongoing debate about what exactly intelligence encompasses.

2. History of Intelligence Testing

• Francis Galton (late 1800s): First broad attempts at intelligence testing focusing on sensory and motor skills.

• Alfred Binet (early 1900s): Commissioned by the French government to develop a test to identify children needing educational assistance.

  • Developed tests emphasizing verbal tasks.

  • His test was the first practical intelligence test.

• Lewis Terman (Stanford-Binet, 1916):

  • Adapted Binet’s test for use in the U.S.

  • Standardized administration and scoring.

  • Normed test on large representative samples to create average scores by age.

  • Established the bell curve (normal distribution) of IQ scores.

  • The Stanford-Binet is still in use today in updated versions.

• David Wechsler (1939):

  • Developed the Wechsler-Bellevue Intelligence Scale for adults, combining verbal and performance subtests.

  • Emphasized intelligence as a global capacity to think rationally and act purposefully.

  • Tests later renamed as Wechsler Adult Intelligence Scale (WAIS), Wechsler Intelligence Scale for Children (WISC), and Wechsler Preschool and Primary Scale of Intelligence (WPPSI).

  • Consists of several subtests covering verbal comprehension, visual spatial skills, fluid reasoning, working memory, and processing speed.

  • Tests are periodically normed and standardized.

3. Standardization and Norming

• Standardization: Ensures consistent administration, scoring, and interpretation of tests to produce reliable results.

• Norming: Test is given to a large sample representing the population; results establish normative scores for interpretation.

• Norms describe what groups typically score, allowing individual scores to be meaningfully compared.

4. Scoring and Distribution

• IQ scores follow a bell curve (normal distribution).

• The average IQ is set at 100; standard deviation is typically 15 points.

• Score ranges:

  • 85–115 IQ: Average (about 68% of the population falls here).

  • 130 and above: Superior/gifted intelligence (~2% of the population).

  • Below 70: Intellectual disability (~2.2% of the population).

5. Diagnosis of Intellectual Disability

• Defined not simply by IQ below ~70, but also significant deficits in adaptive functioning (e.g., communication, self-care).

• Must be present before age 18.

• Subtypes: Mild (85%), Moderate (10%), Severe (5%), Profound (<1%), varying in severity of adaptive needs.

6. Flynn Effect

• Named after James Flynn who identified the gradual rise in measured IQ scores generation after generation worldwide.

• Suggests improvements likely due to environmental factors (education, nutrition).

• Does not necessarily imply each generation is inherently more intelligent.

7. Purposes and Benefits of IQ Testing

• Identify children needing educational support or accommodations.

• Assist in diagnosing intellectual disabilities.

• Help courts determine competency or special circumstances (e.g., Atkins v. Virginia ruling on intellectual disability and capital punishment).

• Used in research and clinical settings for assessment of cognitive function.

• Provides standardized data useful for educational planning and social services.

8. Limitations, Controversies, and Ethical Considerations

• Limitations:

  • IQ tests primarily measure certain cognitive skills and may underrepresent other intelligences (emotional, creativity, practical skills).

  • Debate exists about cultural biases in IQ tests.

  • IQ scores alone do not capture an individual’s full potential or worth.

• Controversies:

  • Historical misuse in eugenics movements and forced sterilizations (e.g., Buck v. Bell case).

  • Social and ethical implications of labeling and classification.

  • Risk of stigmatization or misuse in legal and educational settings.

• Ethical administration: Only trained psychologists may administer IQ tests today; usage is regulated and monitored.

9. Notable Case Example: Atkins v. Virginia

• Supreme Court ruled it unconstitutional to execute persons with intellectual disabilities.

• Intellectual disability was evidenced by IQ and deficits in adaptive skills.

• Highlights legal and ethical importance of intelligence testing in justice.

Summary Table: IQ Testing Essentials