intelligence quotient (IQ)
/ in-TEL-ih-juns KWOH-shunt /
An intelligence quotient, or IQ, is a single number that says how your performance on a particular kind of mental test compares to everyone else's. The test is scored, then stretched onto a scale where 100 is the dead-centre average — set there by design, so that roughly half the population scores above it and half below. So an IQ isn't a measure of how clever you are in some absolute sense; it's more like your ranking in a very specific race, run against the rest of the crowd.
Why bother? Because, narrow as it is, that score is surprisingly useful. It does a decent job of predicting how someone will fare at school or at certain jobs, and it flags learning difficulties early enough to help. Picture a thermometer: a single reading that's genuinely informative, yet tells you nothing about the whole weather system around it.
Here's the trap to avoid: IQ measures one slim slice of the mind — chiefly reasoning, pattern-spotting, and verbal skill under timed conditions. It says little about creativity, wisdom, emotional savvy, drive, or street smarts. Scores can drift with schooling, practice, language, and culture, and the whole idea has a tangled, often abused history. A high IQ is a real strength; it is not a verdict on a person's worth or their ceiling.
On the standard scale about 68% of people score between 85 and 115, and only about 1 in 1,000 scores above 145 — the score is a position in the crowd, not a fixed property of a brain.
How IQ scores spread across a population.
The term "intelligence quotient" comes from an early formula — mental age divided by actual age — proposed in 1912; multiplying that ratio by 100 to give the familiar three-digit scale came a few years later. Modern tests dropped the ratio but kept the name and the 100-is-average idea. Across the 20th century raw scores crept steadily upward worldwide (the "Flynn effect"), a reminder that the number reflects environment, not just inborn wiring.