Intelligence and IQ
IQ is one of the most heavily studied constructs in psychology — both robustly predictive and frequently misunderstood. Understanding what it captures and what it misses matters.
Key facts
- g is among the most replicated findings in psychology.
- IQ correlates ~0.5 with educational attainment.
- Flynn effect: ~3 IQ points per decade in 20th century.
- IQ misses creativity, motivation, emotional intelligence, expertise.
The g Factor
Spearman's g — the positive correlation across diverse cognitive tests — is among the most replicated findings in psychology. Modern factor models include fluid intelligence (Gf) and crystallized intelligence (Gc) as broad components.
What IQ Predicts
IQ predicts educational attainment, occupational complexity, and many health and life outcomes — meaningfully but imperfectly. Effect sizes are smaller than popular accounts suggest.
What IQ Misses
IQ does not capture creativity at the highest levels, social and emotional intelligence, motivation, conscientiousness, or domain expertise — all of which independently predict real-world success.
The Flynn Effect
Measured IQ rose ~3 points per decade through most of the 20th century in industrialized countries. The increase has slowed or reversed in recent decades, with mechanisms still debated.
Frequently asked
Is IQ genetic?
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Heritability estimates of ~50–80% in adulthood — but heritability is not destiny, and reflects population-level variance under specific environments.
Can IQ be raised?
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Education raises measured IQ. Targeted training raises specific subtest scores but rarely transfers broadly.
Sources & further reading
Continue in this series
Biological Substrate
The Neuron and the Brain
Sensory Cognition
Perception and Attention
Storage and Recall
Memory Systems
Higher Cognition
Reasoning and Decision-Making
Communication
Language and Symbolic Thought
Subjective Experience
Consciousness: The Hardest Problem