Quick Answer
IQ (Intelligence Quotient) is a standardized score that measures specific cognitive abilities - reasoning, working memory, processing speed, and spatial thinking. It does not measure creativity, emotional intelligence, or wisdom. The average score is 100 with a standard deviation of 15.
Definition and origin
The term "Intelligence Quotient" was coined by German psychologist William Stern in 1912. The original formula divided mental age by chronological age and multiplied by 100 - a "ratio IQ." A 10-year-old performing like a 12-year-old had a ratio IQ of 120.
Modern IQ tests use "deviation IQ" instead. Rather than comparing mental to chronological age, your score reflects how far above or below the average for your age group you fall. The mean is fixed at 100 and the standard deviation at 15.
A brief history
Alfred Binet created the first practical intelligence test in 1905 for the French government, designed to identify children who needed extra educational support. Lewis Terman at Stanford adapted it as the Stanford-Binet in 1916, which became the dominant test in the US.
David Wechsler introduced the Wechsler-Bellevue Intelligence Scale in 1939, which split intelligence into verbal and performance components. His updated versions - the WAIS for adults and WISC for children - remain the gold standard clinical assessments today.
What IQ tests actually measure
- Fluid intelligence - solving novel problems without prior knowledge
- Crystallized intelligence - applying learned knowledge and vocabulary
- Working memory - holding and manipulating information in the short term
- Processing speed - how quickly you perform simple cognitive tasks
- Spatial reasoning - mentally rotating and manipulating shapes and patterns
Different tests weight these components differently. The WAIS-IV measures all five in separate subtests and combines them into a Full Scale IQ. Raven's Progressive Matrices tests only fluid intelligence and spatial reasoning, making it more culturally neutral.
What IQ doesn't measure
- Creativity and artistic ability
- Emotional intelligence (EQ) - reading and managing emotions
- Practical intelligence - navigating real-world situations
- Social skills and interpersonal effectiveness
- Wisdom - applying experience and judgment to complex situations
- Moral reasoning and ethical judgment
Howard Gardner's theory of multiple intelligences (1983) proposed that human intelligence includes at least 8 distinct types - linguistic, logical-mathematical, spatial, musical, bodily-kinesthetic, interpersonal, intrapersonal, and naturalist. Standard IQ tests capture only the first three.
The normal distribution explained
IQ scores follow a bell curve. Most people cluster around 100. Each step of 15 points represents one standard deviation. About 68% of people score between 85 and 115 (within 1 SD). About 95% score between 70 and 130 (within 2 SD). Only 0.3% score below 55 or above 145.
Different IQ tests and their accuracy
| Test | Type | Use Case | Accuracy |
|---|---|---|---|
| WAIS-IV | Clinical | Adult assessment, diagnosis | High - gold standard |
| Stanford-Binet 5 | Clinical | All ages, gifted testing | High - gold standard |
| Raven's Progressive Matrices | Research / Clinical | Culture-fair reasoning | High for fluid IQ |
| Mensa Workout | Practice | Mensa qualification prep | Low - not official |
| Online IQ tests | Entertainment | Quick self-assessment | Moderate (±5-10 pts) |
Online tests like the one on this site provide a reasonable estimate of your cognitive ability in the domains they test. They are not substitutes for clinical assessments but are more accurate than they are often given credit for, particularly on pattern recognition and logical reasoning tasks.
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