NUMBAT OER - Open Educational Resources

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

Error plot examples
Figure 1. Examples of error plots comparing two samples with differing degrees of overlap
(Source: Ruckstuhl, KE and Festa-Bianchet, M (1998) Do reproductive status and lamb gender affect the foraging behaviour of bighorn ewes? Ethology 104 941-54.)

A box plot would also be a suitable way to present the data, and is used in the example used in the report.

Example box plot
Figure 2. Example box plot of data from the example study. Sample 14 (ewe 945) is shown as an outlier

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 for the difference data from the example study