Give an intelligence test to thousands of people and the scores fan out into a familiar shape: most cluster near the middle, few land at the extremes — a normal distribution, or bell curve. Slide a score to see where it falls, then flip to the dartboard to learn the two questions we ask of any test: is it reliable, and is it valid?
IQ on the normal curve
IQ score100
68% of scores fall in 85–115 · 95% in 70–130 · 99.7% in 55–145
Each dartboard is one test. The bullseye is the true thing you want to measure.