Boxplots or Box and Whisker Diagrams

A box-and-whisker plot or boxplot is a visual display of some of the five figure summary of a data set. It shows the minimum value,the lower quartilethe medianthe upper quartileand the maximum value

For the data set 2, 4, 4, 6, 7, 8, 12, 13, 17, 17, 18

and

The list is 11 long.which rounds up to 3 so the lower quartile is the third number:

To find the upper quartilecalculatewhich rounds up to 9 so the upper quartile is the ninth number and

To find the median,so the median is the average of the fifth and sixth numbers:

The boxplot is shown below.

The rectangular box represents the ‘middle’ half of the data set.

The lower whisker represents the 25% of the data with smallest values.

The upper whisker represents the 25% of the data with greatest values.