From the median simulation
(section 5 of this chapter), we saw that the middle number of
a dataset minimizes the sum of the absolute deviations from the
other numbers. This middle number is called the "median"
and is a frequently used measure of central tendency. By definition,
half of the values in a distribution are above the median and
half are below. Thus, the median is the midpoint of a distribution.

Computation of the Median

When there is an odd number of numbers, the median
is simply the middle number. For example, the median of 2, 4,
and 7 is 4. When there is an even number of numbers, the median
is the mean of the two middle numbers. Thus, the median of the
numbers 2, 4, 7, 12 is (4+7)/2 = 5.5.