Statistics for Ecologists Using R and Excel by Gardener Mark;

Author:Gardener, Mark; [Mark Gardener]
Language: eng
Format: epub
ISBN: 1686146
Publisher: Pelagic Publishing

10. Differences between more than two samples

The differences and correlation tests that we have covered so far have looked at two samples. The t-test (Section 7.1) and U-test (Section 7.2) look for differences between two sets of data for example. The Spearman’s rank test (Section 8.1) and Pearson’s product moment (Section 8.2) look for a correlation between two variables.

It is quite common to want to examine more than two sites or to look at more than two factors. In most cases you will be looking at a single dependent variable, this might be the abundance of a plant or invertebrate species. You might look at differences in abundance between several sites or you may look to see how several environmental factors affect the abundance of a species. In these cases we need to use some form of analysis of variance (for looking at differences, see Sections 10.2 and 10.3) or multiple regression for correlations (see Chapter 11).

We may still use the same kinds of graphs to help us make sense of the data (see Chapter 6) using box–whisker plots for example; however, our graphs will be rather more complex, depending on the complexity of the situation we are describing.

When you have several independent factors (probably species abundances) and also several factors we talk about multivariate analyses. The approach for these multivariate analyses is rather more complex and won’t be covered in this book (community analyses will be dealt with in a separate volume).

Download

Copyright Disclaimer:
This site does not store any files on its server. We only index and link to content provided by other sites. Please contact the content providers to delete copyright contents if any and email us, we'll remove relevant links or contents immediately.