Measures of Central Tendency - The Median

The median is the middle value in distribution when the values are arranged in ascending or descending order.

The median divides the distribution in half (there are 50% of observations on either side of the median value). In a distribution with an odd number of observations, the median value is the middle value. 

Looking at the retirement age distribution (which has 11 observations), the median is the middle value, which is 57 years: 

54, 54, 54, 55, 56, 57, 57, 58, 58, 60, 60 

When the distribution has an even number of observations, the median value is the mean of the two middle values. In the following distribution, the two middle values are 56 and 57, therefore the median equals 56.5 years: 

52, 54, 54, 54, 55, 56, 57, 57, 58, 58, 60, 60