2.3 Dispersion on box plots

Here is the boxplot from Activity 5 again.

Figure 7 Box plot of rainfall, dispersion measures labelled

Since the box goes from the lower to the upper quartile, the length of the box represents the interquartile range (IQR).

Also, since the ‘whiskers’ go from the minimum to the maximum value, the total length of the plot represents the range of the data.

The values for both dispersion measures have been calculated from the summary statistics table, not reading the scale on which the boxplot is given since that is not detailed enough in this instance.

If you plot multiple box plots on the same set of axes, it is possible to make quick visual comparisons of data sets involving the key statistics represented.