The median (also called the 2nd quartile or 50th percentile) is the midpoint of the data set: half the observations are above it, half are below it. It is determined by ranking the data and finding observation number [N + 1] / 2. If there are an even number of observations, the median is extrapolated as the value midway between that of observation numbers N / 2 and [N / 2] + 1.

The median is less sensitive to extreme values than the mean. Therefore, the median is often used instead of the mean when data contain outliers, or are skewed.

In the precipitation data set, there are 11 (non-missing) observations. Thus, the median is the value of the 6th highest (or 6th lowest) observation, which is 3:

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Notice the median of this data set would be 3 even if there were 30 days with precipitation in April instead of 10.