Percentiles divide a set of data into 100 equal parts, each consisting of 1 percent of the total. For example, if a student’s score on a standardized exam (such as the ACT or GRE) is in the 90th percentile, then the student outscored 90 percent of the other students who took the exam. A quartile is a special type of percentile; it divides a data set into four equal parts, each consisting of 25 percent of the total. The first quartile is the 25th percentile of a data set, the second quartile is the 50th percentile, and the third quartile is the 75th percentile. The interquartile range identifies the middle 50 percent of the observations in a data set; it equals the difference between the third and the first quartiles.
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Last Modified: 07/02/2018