Sunday, 13 March 2016

Box and whisker plots

A box and whisker plot is used to display information about the range, the median and the quartiles. It is usually drawn alongside a number line, as shown -
A diagram composed of a rectangle with a non-mid centre line dividing it into two unequal parts, with one horizontal line coming out of each end, and a scale with no values on underneath. The box diagram has various labels on. The left end of the left line says 'this whisker shows the lowest value'. The left edge of the rectangle says 'This line shows the lower quartile'. The line dividing the rectangle says 'This line shows the median'. The right edge of the rectangle says 'This line shows the upper quartile'. The right end of the right line says 'This whisker shows the highest value.' Both ends of the rectangle are labelled 'The width of the box shows the interquartile range'.

Example

The oldest person in Mathsminster is 90. The youngest person is 15.
The median age of the residents is 44, the lower quartile is 25, and the upper quartile is 67.
Represent this information with a box-and-whisker plot.

Solution

A box plot diagram. An essentially horizontal rectangle is divided into two unequal parts by a vertical line, and two horizontal lines stick out the left and right edges. Below this is a scale going from zero to 100 in multiples of 10.
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