quartile

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.