IQ, or Intelligence Quotient, is a numerical score derived from a set of standardized tests designed to assess human intelligence. The abbreviation "IQ" was coined by the psychologist William Stern for the German term Intelligenzquotient, his term for a scoring method for intelligence tests at University of Breslau in 1912.
History of IQ Testing
Historically, even before IQ tests were invented, there were attempts to classify people into intelligence categories by observing their behavior in daily life. Those attempting to establish a behavioral norm largely failed in typical cases.
Paul Broca & Sir Francis Galton
Researchers like Paul Broca (1824-1880) and Sir Francis Galton (1822-1911) believed that intelligence could be determined by measuring the size of the human skull. They assumed that a larger skull meant a larger brain, and thus, higher intellectual capability. However, this theory was later disproven.
Alfred Binet: The Father of Modern Testing
The first modern intelligence test was developed in 1904 by Alfred Binet (1857-1911) and Theodore Simon. The French Ministry of Education commissioned them to create a method to distinguish children who were intellectually challenged from those who were merely lazy, to ensure they received appropriate education.
Binet developed the concept of "Mental Age". For example, if a 6-year-old child passed tasks typically solvable by an 8-year-old, their mental age was 8.
"Intelligence is the faculty of adapting one's self to circumstances." — Alfred Binet
How is IQ Calculated?
Originally, IQ was calculated as a ratio of Mental Age to Chronological Age, multiplied by 100:
IQ = (Mental Age / Chronological Age) × 100
For instance, a 10-year-old with a mental age of 13 would have an IQ of 130. While this worked for children, it was flawed for adults.
Deviation IQ (Modern Method)
Today, tests (like the one on this website) use Deviation IQ. This method compares a person's score against the average score of a large population sample of the same age. The scoring is calibrated to a Gaussian Bell Curve.
The Bell Curve Distribution
IQ scores are distributed such that the majority of people score near the average.
- 100 is defined as the average score.
- 85 to 115 covers roughly 68% of the population (average intelligence).
- Above 130 is considered "Gifted" (Top 2%).
- Below 70 may indicate developmental challenges.
[Gaussian Distribution Graph Visualization]
What Does IQ Measure?
Modern IQ tests, particularly those based on Raven's Progressive Matrices (like ours), focus on:
- Fluid Intelligence: The ability to solve novel problems, use logic, and identify patterns independent of acquired knowledge.
- Abstract Reasoning: Visualizing complex relationships between shapes and figures.
Unlike "Crystallized Intelligence" (facts and knowledge), Fluid Intelligence is less influenced by culture or education, making it a fair measure of raw cognitive potential.