Math & Statistics · 百分位数 · Updated 2026-10-25
What Is Percentile?
Definition
The p-th percentile is the value below which p% of data falls. P50 is the median; P25–P75 form the IQR; growth charts and lab reference ranges are percentiles.
Formula
IQR = P75 − P25; reference range: P2.5–P97.5
Worked Example
A baby at P70 for length is taller than ~70% of peers — a position, not a score. Stability along one’s own percentile matters most.
Common Misconception
"P90 scores 40 points above P50" - percentiles are positions, not scores; the raw gap depends on distribution shape. "P5 is always abnormal" - it depends on the metric: height P5 may be genetic, kidney-function P5 needs follow-up.
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