Quartile. 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.