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Quartile is a rank-order grouping. A quartile divides a distribution of data into four equally sized groups determined after ranking the data according to some measure or combination of measures.

There is some debate about who first used the term quartile (contenders include Carl F. Gauss, Donald McAlister, and Francis Galton), but it seems that Galton was the first to bring the terms quartile, decile, and percentile into common use.

The term quartile can have two meanings: a point on the distribution that divides the four groups, and the group to which a member of the distribution belongs. There are three decile values, which separate the data into the four groups. The third decile value (commonly known as the upper quartile) is the point in the ...

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