How is intelligence defined, measured, and influenced by heredity and environment?
Topic 2.8 Intelligence and Achievement: explain theories of intelligence, how intelligence and achievement are measured, and the role of heredity, environment, and bias in testing.
A focused answer to AP Psychology Topic 2.8, covering theories of intelligence (general intelligence, multiple intelligences, triarchic theory), the construction and standardization of intelligence tests, reliability and validity, the normal curve, and the influence of heredity, environment, and test bias.
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What this topic is asking
Topic 2.8 closes Unit 2 with intelligence and achievement. The College Board wants you to compare theories of intelligence, explain how tests are constructed and standardized, define reliability and validity, interpret the normal curve, and weigh the influence of heredity, environment, and bias on intelligence scores.
Theories of intelligence
Spearman's g is supported by the tendency of people who do well on one mental task to do well on others. Gardner and Sternberg broaden the concept to include abilities a single number can miss. The exam also distinguishes fluid intelligence (reasoning quickly, which declines with age) from crystallized intelligence (accumulated knowledge, which holds or grows).
Measuring intelligence
Intelligence tests have a long history, from Binet's mental age to the modern Stanford-Binet and Wechsler scales. A good test must meet three standards:
A test can be reliable without being valid (consistently measuring the wrong thing), but it cannot be valid without being reliable.
The normal curve
Standardized intelligence scores typically form a normal distribution (a symmetric, bell-shaped curve): most scores cluster near the average (set at 100), and progressively fewer scores fall toward the extremes. The normal curve lets psychologists describe where any score falls relative to the population.
Heredity, environment, and bias
Intelligence reflects both heredity and environment (recall Topic 1.1). Twin and adoption studies show genetic influence, while enriched environments, nutrition, and education raise scores; the rising scores across generations (the Flynn effect) point to environmental influence. Crucially:
- Heritability of intelligence describes variation within a population, not the cause of differences between groups, which can reflect environment.
- Tests can show bias if their content or language favors one group, so scores must be interpreted with care and never treated as a fixed measure of innate worth.
This topic ties Unit 2 back to Unit 1 and forward to the rest of the course. Intelligence is a cognitive capacity, so it belongs in the cognition unit, but it is shaped by the same nature-nurture interaction that opened the biological unit, which is why the heritability cautions from Topic 1.1 reappear here. The measurement concepts, standardization, reliability, validity, and the normal curve, are not just about intelligence; they are the foundations of psychological testing that recur whenever the course discusses assessment. For the exam, the most heavily rewarded skills are distinguishing reliability from validity, explaining why a heritability estimate cannot explain group differences, and recognizing that an intelligence score is a snapshot influenced by environment and possible bias, not a fixed verdict on a person.
Try this
Q1. Distinguish reliability from validity. [2 points]
- Cue. Reliability is the consistency of a test's scores; validity is whether the test actually measures and predicts what it claims to.
Q2. Explain why a heritability estimate for intelligence cannot explain differences between two groups. [1 point]
- Cue. Heritability describes how much variation within a population is due to genes; differences between groups can result from different environments, so heritability does not apply.
Exam-style practice questions
Practice questions written in the style of College Board exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
AP 2023 (style)1 marksMultiple choice. A psychologist gives the same intelligence test to a group of people twice, several weeks apart, and finds that their scores are very consistent across the two administrations. This finding indicates that the test has high (A) content validity (B) predictive validity (C) standardization (D) test-retest reliability (E) cultural fairnessShow worked answer →
The answer is (D) Test-retest reliability.
Test-retest reliability is the consistency of a test's scores when the same people take it on different occasions. Consistent scores across two administrations indicate the test reliably measures whatever it measures.
(A) content and (B) predictive validity concern whether a test measures and predicts what it should, not consistency. (C) standardization is establishing uniform procedures and norms. (E) cultural fairness concerns bias. Only test-retest reliability describes consistency across repeated testing.
AP 2022 (style)6 marksConcept-application free-response question. A school district introduces a new intelligence test. Explain how EACH of the following applies to evaluating and using the test: standardization, the normal curve, reliability, validity, Spearman's general intelligence (g), and the influence of environment on intelligence scores.Show worked answer →
A 6-point concept-application FRQ; one point per term.
Standardization (1): the test must be administered and scored uniformly and normed on a representative sample so scores are comparable.
Normal curve (1): standardized scores typically form a bell-shaped distribution, with most scores near the average and few at the extremes.
Reliability (1): the test must produce consistent scores (for example test-retest reliability) to be trustworthy.
Validity (1): the test must actually measure intelligence and predict relevant outcomes (content and predictive validity).
Spearman's general intelligence g (1): the test may assume a single underlying general intelligence factor that influences performance across tasks.
Environment (1): environmental factors (schooling, nutrition, enrichment) influence scores, so differences may reflect environment, not innate ability.
Markers reward each term being correctly defined AND applied to evaluating the new test.
Related dot points
- Topic 2.2 Thinking, Problem-Solving, Judgments, and Decision-Making: explain concepts and prototypes, problem-solving strategies, and the heuristics and biases that shape judgment.
A focused answer to AP Psychology Topic 2.2, covering concepts and prototypes, algorithms and heuristics, insight and fixation, and the judgment biases (availability, representativeness, anchoring, framing, confirmation bias) that distort decision-making.
- Topic 2.3 Introduction to Memory: describe the major models of memory, including the three-stage information-processing model and the different memory systems.
A focused answer to AP Psychology Topic 2.3, introducing the three-stage information-processing model (sensory, short-term, long-term memory), working memory, the multi-store and levels-of-processing models, and the distinction between explicit and implicit memory.
- Topic 2.1 Perception: explain bottom-up and top-down processing, perceptual organization and constancies, depth and gestalt principles, and the influence of attention and set.
A focused answer to AP Psychology Topic 2.1, covering bottom-up and top-down processing, gestalt grouping principles, depth cues, perceptual constancies, selective attention, perceptual set, and how prior knowledge shapes what we perceive.
- Topic 1.1 Interaction of Heredity and Environment: explain how the interaction of nature and nurture, studied through twin, family, and adoption research, shapes psychological traits.
A focused answer to AP Psychology Topic 1.1, covering the nature-nurture interaction, heritability, the evolutionary perspective, and how twin, family, and adoption studies let psychologists separate genetic from environmental influences on behavior.
- Topic 2.4 Encoding Memories: explain the processes of encoding information into memory, including effortful and automatic processing, levels of processing, and mnemonic strategies.
A focused answer to AP Psychology Topic 2.4, covering automatic and effortful processing, the levels-of-processing effect, semantic encoding, mnemonic devices, chunking, the spacing effect, and the self-reference and testing effects that strengthen encoding.
Sources & how we know this
- AP Psychology Course and Exam Description — College Board (2024)