quantity

Percentile

A statistical measure indicating the value below which a given percentage of observations fall.
9 related articles

Description

A percentile is a way to understand where a particular value sits within a larger set of data. If you score in the 90th percentile on a test, it means you did better than 90 percent of the people who took it — not that you got 90 percent of the questions right. Percentiles are used everywhere from standardized testing to growth charts for children, helping to compare a single observation against a whole population.

History

The concept was formalized in the late 19th century by Francis Galton, who used it to analyze variation in human traits.

How it works

To find the percentile of a value, you first sort all the data from smallest to largest. Then you count how many observations fall below that value, divide by the total number of observations, and multiply by 100. The result tells you the percentage of the data that lies beneath that point. For example, if 25 out of 100 measurements are smaller than your value, that value is at the 25th percentile.

In practice

Percentiles are used in medicine to track infant growth, in finance to assess risk (e.g., value at risk), and in climate science to define extreme events like heatwaves or heavy rainfall.

Fun fact

The 50th percentile is exactly the median — half the data lies above it and half below it.

Concept graph →

Related articles · 9

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