One of the four divisions of observations which have been grouped into four equal-sized sets based on their statistical rank. The quartile
including the top statistically ranked members
is called the first quartile and denoted . The other quartiles are similarly denoted , ,
and . For data points with of the form (for , 1, ...), the hinges are identical
to the first and third quartiles.

The following table summarizes a number of common methods for computing the position of the first and third quartiles from a sample size (P. Stikker, pers. comm., Jan. 24,
2005). In the table,
denotes the nearest integer function.