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Definition: quartile from BUSINESS: The Ultimate Resource

any of the values in a frequency or probability distribution that divide it into four equal parts


Summary Article: quartile
from The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide

In statistics, any one of the three values that divide data into four equal parts. They comprise the lower quartile, below which lies the lowest 25% of the data; the median, which is the middle 50%, half way through the data; and the upper quartile, above which lies the top 25%. The difference of value between the upper and lower quartiles is known as the interquartile range, which is a useful measure of the dispersion of a statistical distribution because it is not affected by freak extreme values (see range). These values are usually found using a cumulative frequency diagram.

For example, a football team scored the following goals in one season:

This information can be displayed in a cumulative frequency curve:

From the curve, the median is 2.4 goals, the lower quartile is 1.2 goals, and the upper quartile is 3.4 goals. The interquartile range is 3.4 − 1.2, which is 2.2 goals.

The lower quartile may also be described as the 25th percentile; the median as the 50th percentile; and the upper quartile as the 75th percentile.

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Cumulative frequencies and medians

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