NUMBAT OER - Open Educational Resources

Since this is a parametric test, an error plot is an appropriate presentation of the data and is used in the example report. It shows the mean and variance of the samples being compared and is a clear way of demonstrating the degree of overlap between samples.

Bone density graph
Figure 1. Error plots of example data, showing 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)
Error plot examples
Figure 2. Examples of error plots comparing two samples with differing degrees of overlap

As part of the check that data satisfy the parametric criteria, it may be appropriate to plot out the data for each sample as a histogram to assess the closeness of the distribution to a normal distribution. This would not apply to small samples.

Example histogram
Figure 3. Example histogram