Definition
The value of the smallest observation in the highest 25% of a data set. 75% of the points in a data set are equal to or less than this value. It is also called the 'third' or 'upper' quartile of the dataset.
Examples
![](/pics/quartiles.gif)
There are three quartiles, dividing the data set into four equal parts. They are shown below for a data set with 10 values: 49, 15, 3, 51, 12, 26, 60, 12, 17, 7.
Application
The distance between the third (upper) and first (lower) quartiles is called the Inter-Quartile Range (IQR). The IQR is represented by the 'box' in a boxplot.