Official IQ Test
Interactive Timeline

The Evolution of
the Measurement of Intelligence

Discover more than 140 years of scientific revolutions, from Galton's first hypotheses to the most sophisticated contemporary theories.

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Timeline

More than 120 years of science

  • • Galton (1883)
  • • Binet (1905)
  • • Wechsler (1939)
1904

Charles Spearman

The g Factor

calculate

“General intelligence is a unique biological faculty.”

1905

Alfred Binet

The Origin (France)

Alfred Binet portrait

First practical intelligence test for schoolchildren.

1916

Lewis Terman

Stanford-Binet

IQ = (MA/CA) × 100
1917

Army Alpha/Beta

Mass Assessment

groups

Used to classify 1.7 million US recruits.

1939

David Wechsler

WAIS (Modern IQ)

analytics

Introduction of IQ by statistical deviation.

1983

Multiple Intelligences

H. Gardner

Key Moments in History

A detailed timeline of discoveries that transformed our understanding of human intelligence.

1884

Francis Galton and Biometrics

The Forerunner

calculate

Cousin of Charles Darwin, Galton established the first "Anthropometric Laboratory" in London. It attempts to measure intelligence by sensory finesse and reaction time. Although his tests were imperfect, he revolutionized statistics by inventing correlation and regression.

1904

Charles Spearman & the g Factor

The Statistical Foundation

functions

Spearman publishes groundbreaking research on general intelligence. It statistically demonstrates that if a person passes a logic test, they tend to pass all other cognitive tests. He calls this common mental energy the famous "g factor" – the general intelligence factor.

1905

The Binet-Simon Scale

The Practical Birth

school

Alfred Binet and Théodore Simon create the first objective method to measure “Mental Age”. The objective was to identify children in need of special support in the French school system. Binet insisted that intelligence is not fixed and can be increased through education and training.

1912

William Stern & the "Quotient"

The Magic Formula

balance

German psychologist William Stern proposed a revolutionary change: divide mental age by chronological age to obtain a constant ratio. He invented the now universal acronym I.Q. (Intelligenz-Quotient). This simple formula transformed how intelligence is measured.

1917

Army Alpha & Beta Tests

The Showdown

groups

During World War I, Robert Yerkes developed tests for the American army. The "Beta" was revolutionary because it was non-verbal, allowing illiterate or non-English speaking recruits to be tested. This is the start of large-scale collective testing: 1.7 million recruits tested.

1939

David Wechsler & the WAIS

The Modern Standard

analytics

Wechsler criticizes the concept of mental age for adults. He creates the deviation IQ: we compare the individual to their age group, not to a fixed formula. A score of 100 becomes exactly the average. The WISC (children) and the WAIS (adults) remain the global benchmarks today, used in more than 70 countries.

1983 - Today

The Age of Multiple Intelligences

Broadening

lightbulb

The emergence of theories such as Gardner's Multiple Intelligences, Goleman's Emotional Intelligence and Sternberg's Triarchic Theory questioned the uniqueness of IQ. However, standardized psychometric tests remain the most accurate tool for predicting cognitive, academic, and professional success.

Fundamentals

Why measure
intelligence?

At the beginning of the 20th century, school became compulsory. The challenge was to objectively identify students in need of special support. What began as an educational tool became the basis of modern psychometrics and influenced global education.

100 Average (Median)
σ 15 Standard deviation
68% Between 85-115

IQ Distribution

Gaussian distribution (bell curve)

insights
Bell curve showing the IQ score scale
Rare (< 2.2%) Extremes
Common (13.6%) Above/below average
Very common (68%) Core population

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