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.
Cumulative frequencies and medians
Box and Whiskers Plots
O bservations can be grouped into four equalsized sets according to their rank order . Each of the four sets forms a quartile, which is a...
1 One of the three points that divide an ordered distribution into four parts each containing one quarter of the scores. 2 One of...
/kwawtiel/ noun in statistics, any of three numbers that divide a frequency distribution into four groups with equal frequencies, or any...