The median of the upper half of a set of data is the upper quartile (UQ) or Q3 . The upper and lower quartiles can be used to find another measure of variation call the interquartile range. The interquartile range is the range of the middle half of a set of data. It is the difference between the upper quartile and the lower quartile. Interquartile range = Q3 – Q1 In the above example, the lower quartile is 52 and the upper quartile is 58. The interquartile range is 58 – 52 or 6. Data that is more than 1.5 times the value of the interquartile range beyond the quartiles are called outliers .