NUMBAT OER - Open Educational Resources

Since this is a nonparametric test, a box plot is an appropriate presentation of the data. A box plot is constructed for each sample in order to compare them.

Two box plots example
Figure 1. Example of two box plots used to compare samples, in this case bone densities in men and women
(Data from Liz Smith, MRC Human Nutrition Research Laboratory, cited in Hawkins, D (2009) Biomeasurement 2nd edition. Oxford University Press, Oxford)

The different elements of the box plot are indicated here:

Single box plot example
Figure 2. Example of a single box plot output by SPSS, with extreme values and outliers indicated separately

An error plot may also be appropriate for this sort of data, and is used in the example report. It shows the mean and variance of the samples being compared and, like the box plot, is a clear way of demonstrating the degree of overlap between samples.

Bone density graph
Figure 3. The data from Figure 1 as error plots, with mean values and confidence intervals
(Data from Liz Smith, MRC Human Nutrition Research Laboratory, cited in Hawkins, D (2009) Biomeasurement 2nd edition. Oxford University Press, Oxford)