Interquartile range (IQR)
SAT glossary · Math
Definition
Q3 -Q1, the width of the middle 50% of the data. A value is an outlier if it lies more than 1.5 × IQR beyond either quartile.
Interquartile range (IQR) in plain English
The interquartile range (IQR) measures how spread out the MIDDLE half of your data is, by taking the top quartile (Q3, where the top 25% of data begins) and subtracting the bottom quartile (Q1, where the bottom 25% ends): IQR=Q3-Q1. It deliberately ignores the most extreme values at either end, focusing only on the central chunk of the data. This makes it useful for spotting outliers too — there's an official rule that any data point sitting more than 1.5timesIQR beyond either quartile counts as an outlier, a value unusually far from the rest of the pack.
Also called: IQR
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