Theories of intelligence: general intelligence, multiple intelligences and IQ testing (QCE Psychology Unit 2)
“Describe the psychometric approach to intelligence (i.e. intelligence quotient, or IQ); Describe common methods by which intelligence is measured with reference to IQ tests and scales, including Stanford-Binet scale and Wechsler's intelligence scales for adults (WAIS-IV) and children (WISC-V); Discuss the degree to which intelligence tests are valid and reliable”
Spearman proposed a single general intelligence (g) underlying all mental ability, while Gardner's multiple intelligences and Sternberg's triarchic theory argue intelligence is several distinct capacities. Intelligence is measured with standardised tests (Binet, Wechsler) scored against a normal distribution, but these tests must be evaluated for reliability, validity and cultural bias.
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In the QCAA Psychology 2025 syllabus this subject matter sits in Unit 2: Individual behaviour, Topic 1: Intelligence. Units 1 and 2 are the Year 11 foundation: QCAA says students should complete them before beginning Units 3 and 4, but they are not part of the Units 3 and 4 internal assessments or the external assessment. This page was previously filed under Unit 3.
What this dot point is asking
QCAA wants you to explain that intelligence is a contested concept, compare the major theories of what it is, describe how psychologists try to measure it, and evaluate the quality of those measurements in terms of reliability, validity and fairness. Use named theorists and named tests.
The answer
What is intelligence?
Intelligence is broadly defined as the capacity to learn from experience, reason, solve problems and adapt to the environment. The disagreement is over whether it is one general ability or many separate abilities, which shapes how it should be measured.
General intelligence (Spearman)
Charles Spearman (1904) used factor analysis on test scores and found that people who did well on one cognitive task tended to do well on others. He proposed a general intelligence factor, g, underlying all mental performance, plus specific factors (s) for particular tasks. The existence of positive correlations across diverse tests is the central evidence for g, and modern IQ tests are built on this idea.
Multiple intelligences (Gardner)
Howard Gardner (1983) rejected a single g, proposing several relatively independent intelligences, including linguistic, logical-mathematical, spatial, musical, bodily-kinaesthetic, interpersonal, intrapersonal and naturalistic. His evidence included people with brain damage who lose one ability while keeping others, and savants with exceptional skill in one narrow domain. Critics argue some of these are better described as talents than intelligences, and the theory is hard to test empirically.
Triarchic theory (Sternberg)
Robert Sternberg (1985) proposed three types: analytical (academic problem-solving), creative (dealing with novelty) and practical (everyday street smarts). He argued traditional tests measure mainly analytical intelligence and miss practical and creative ability, which matter for real-world success.
Measuring intelligence
- Binet and Simon (1905) created the first practical intelligence test to identify French schoolchildren needing extra help, introducing the idea of mental age.
- The Stanford-Binet test produced the intelligence quotient (IQ), originally mental age divided by chronological age, times 100.
- The Wechsler scales (WAIS, WISC) are the most widely used today, giving separate verbal and performance scores as well as a full-scale IQ.
IQ scores are standardised so that the population mean is 100 with a standard deviation of 15, and scores follow a normal (bell-shaped) distribution, with about 68 percent of people scoring between 85 and 115.
On modern IQ tests the mean is set to 100 and the standard deviation to 15. Because scores are normally distributed, roughly 68 percent of the population falls within one standard deviation (85 to 115) and about 95 percent within two (70 to 130).
Locate the score on the distribution
A client scores 130 on a Wechsler test (mean 100, standard deviation 15). The task is to interpret the score and evaluate how much weight to place on it.
Convert to a position in the population
A score of 130 is two standard deviations above the mean. Because scores are normally distributed, about 95 percent of people fall within two standard deviations (70 to 130), so this client scores at roughly the top 2.5 percent of the population.
Check reliability and validity
Note that the Wechsler scales are highly reliable (consistent on retesting), but reliability is not validity: the test mainly captures analytical ability and, by Sternberg's triarchic theory, may miss the client's practical and creative intelligence.
Add the fairness check
Conclude by flagging cultural bias and the Flynn effect: the score reflects environment and education as well as innate ability, so it should inform, not determine, any decision about the client.
Evaluating tests: reliability and validity
A good test must be both reliable and valid.
- Reliability is consistency: a test is reliable if it gives similar results on retesting (test-retest reliability) or across its items (internal consistency). Major IQ tests are highly reliable.
- Validity is whether the test measures what it claims to. Predictive validity (IQ predicts school performance reasonably well) is one form, but critics question whether tests capture the full breadth of intelligence.
- Cultural bias threatens validity: tests developed in one culture may disadvantage people from another by assuming particular language or knowledge. The Flynn effect, the steady rise in average IQ scores across generations, also shows that scores are sensitive to environment and education, not just innate ability.
Putting it together for an exam
Name the theory and theorist, state the core claim, then evaluate. For measurement questions, name the test, explain standardisation against the normal distribution, then judge reliability, validity and bias.
- Treating IQ as a fixed, innate number
- The Flynn effect and the influence of education show scores are shaped by environment.
- Confusing reliability and validity
- A test can be reliable (consistent) without being valid (measuring the right thing).
- Saying Gardner and Spearman agree
- Spearman argues for one general intelligence; Gardner argues for several independent intelligences.
- Forgetting the normal distribution
- IQ scoring depends on a mean of 100 and standard deviation of 15; without this the score has no meaning.
Exam-style questions
Questions in the style of QCAA exam questions on this dot point, each with a worked answer. They are written by ExamExplained unless tagged "Past paper"; the year shows the paper a question is modelled on.
2022 QCAA-style6 marksCompare Spearman's theory of general intelligence with Gardner's theory of multiple intelligences, and evaluate the evidence each draws on.Show worked answer →
Six marks: each theory with its claim and evidence, plus a comparison.
- Spearman (2 marks)
- Used factor analysis and found positive correlations across diverse cognitive tasks, proposing a single general intelligence factor (g) plus specific factors (s). The positive manifold of correlations is the central evidence.
- Gardner (2 marks)
- Rejected a single g, proposing several relatively independent intelligences (linguistic, logical-mathematical, spatial, musical, bodily-kinaesthetic, interpersonal, intrapersonal, naturalistic). Evidence includes brain-damaged patients who lose one ability while keeping others, and savants.
- Comparison and evaluation (2 marks)
- Spearman is supported by replicable correlational evidence but may oversimplify; Gardner captures human diversity but is criticised because some "intelligences" look like talents and the theory is hard to test empirically.
Markers reward an explicit contrast plus an evaluation of the evidence, not two separate descriptions.
2023 QCAA-style5 marksAn IQ test reports a mean of 100 and a standard deviation of 15. Determine the percentage of the population expected to score between 85 and 115, and evaluate two threats to the validity of intelligence testing.Show worked answer →
Five marks: the calculation, then two validity threats.
- Calculation (1 mark)
- A score of 85 to 115 is within one standard deviation of the mean, so on a normal distribution about 68 percent of the population is expected to fall in this range.
- Cultural bias (2 marks)
- Tests built in one culture can assume particular language or knowledge, disadvantaging people from another culture, so the score may not validly reflect ability.
- The Flynn effect (2 marks)
- The steady rise in average IQ across generations shows scores are sensitive to environment and education, challenging the validity of IQ as a measure of fixed innate ability.
Markers reward the 68 percent figure and two genuine validity threats with reasoning.