Origins: Binet and Simon (1905)
Alfred Binet and Théodore Simon created the first practical intelligence test in France in 1905 — commissioned by the French Ministry of Education to identify children who needed special instruction. The test measured mental age against chronological age. Binet himself explicitly warned it should not be used to label or rank people by innate intelligence.
The IQ Calculation
William Stern in 1912 proposed the Intelligence Quotient: (Mental Age / Chronological Age) × 100. A child performing at their expected level scores 100. Modern IQ tests no longer use this ratio; instead, they compare performance to population norms, where 100 is always set at the average for the test year.
What IQ Tests Actually Measure
Modern tests (Wechsler, Stanford-Binet) measure a range of cognitive abilities: verbal comprehension, working memory, perceptual reasoning, processing speed. They are good predictors of academic performance and, to a lesser degree, occupational performance in cognitively demanding fields. They do not measure creativity, emotional intelligence, practical wisdom, or social skills.
The Flynn Effect
IQ scores have risen substantially in every country measured over the 20th century — by about 3 points per decade. This "Flynn Effect" proves that IQ does not measure fixed biological intelligence; it measures something responsive to education, nutrition, exposure to abstract thinking, and changing test culture.
Limitations
IQ tests are not culturally neutral. Test performance is influenced by familiarity with the test format, language, socioeconomic background, and test anxiety. A high IQ score is a strong predictor of academic success; it is a weaker predictor of life satisfaction, leadership, or creative achievement.
Frequently Asked Questions
What does IQ actually measure?
Modern IQ tests measure verbal comprehension, working memory, perceptual reasoning, and processing speed. They predict academic performance reasonably well but do not measure creativity, emotional intelligence, or practical skills.
What is a good IQ score?
IQ is normed so that 100 is the population average. Scores between 85-115 cover about 68% of the population. Above 130 is considered gifted (about 2% of population). Above 145 is exceptionally rare.
Is IQ genetic?
Twin and adoption studies suggest IQ is moderately to highly heritable in adults (50-80%). However, the Flynn Effect shows that IQ scores have risen substantially across generations, proving that environment, education, and nutrition also have major effects.
