Inter-Quartile Range
 

This measurement considers the values which are more concentrated in the middle of the distribution.

If we remember that the Median is the middle (or halfway) value the quartiles are the values ¼ and ¾ of the way through the distribution.

The inter-quartile range is the difference between the upper quartile (¾ of the way) and the lower quartile (¼ of the way).

This can best be seen by drawing up a cumulative frequency table and graph.