Quartiles

Statistics which divide the observations in a numeric sample into 4 intervals, each containing 25% of the data. The lower, middle, and upper quartiles are computed by ordering the data from smallest to largest and then finding the values below which fall 25%, 50%, and 75% of the data.

The middle quartile is usually called the median.

Quartiles are special cases of percentiles. The lower quartile, median, and upper quartile are the same as the 25th, 50th, and 75th percentiles.

Box and whisker plots provide a graphical summary of a data sample in terms of its quartiles.

See also: Median, Quintile.