General psychology

Percentile

A percentile is a score expressed as the percentage of a reference population that falls below it. A score at the 70th percentile is higher than 70% of that population — not 70% of maximum possible.

Confusing percentile with "percent correct" is the single most common misreading of psychometric results. A 90th percentile IQ test score does not mean "answered 90% of questions correctly" — it means "higher than 90% of same-age testers."