median

The median is the middle value in a set, found after the values are sorted from least to greatest. With an odd count, it is the single middle value; with an even count, it is the average of the two middle values. For 7, 2, 9, 4 and 5, sorting gives 2, 4, 5, 7, 9, and the middle value is 5. The median is resistant to outliers: in 1, 2, 3, 4 and 100 the median is 3, while the mean is 22, so the median describes the typical case when a single value is extreme. The classic error is to read the middle of the unsorted list, which for 7, 2, 9, 4, 5 is 9 — not the median at all. Sort first; the middle value follows. The median is one of the three measures of center, with the mean and the mode.