The ten values 4, 8, 11, 13, 16, 19, 22, 26, 31, 38 are already in ascending order. Taking Q1 as the median of the lower five values and Q3 as the median of the upper five, find the interquartile range.

The lower half is 4, 8, 11, 13, 16 and its median is the 3rd of them, 11; the upper half is 19, 22, 26, 31, 38 with median 26. The interquartile range is Q3 − Q1 = 26 − 11 = 15. The value 34 is the ordinary range, 38 − 4, which a single stray value can inflate — precisely the weakness the interquartile range is designed to avoid, since it measures only the middle half. The value 17.5 is the median of the whole set, (16 + 19)/2, and 7.5 is the quartile deviation, half of the interquartile range.