Worked Example
88
13.3
Interpreting the results
When a Canonical Correspondence Analysis is undertaken a large number of tabbed
sheets of output will be produced. In this section we will use the Dune Meadow data
to take you through the output.
Having undertaken a CCA from the drop down:
we first examine the Variance tab. The mutilple correlation species/environment
scores indicates how much of the variation in species composition is explicable from
the environmental variables. The  figure of 0.9579 for the first axis indicates that we
can account for most of the variation in species composition by taking account of the
environmental variables. The maximum and minimum values for this coefficient are
1.0 and 0 and a value close to 1 indicates that the environmental variables are having
an appreciable effect, this correlation should be viewed with great caution and can be
highly misleading see 
Problems with Species Environment Correlation
. Note also that
the first canonical axis explains about 21% of the total variability. This is quite a large
amount but may not be significant. A 
Monte Carlo test
 must be used to test for
significance.
The results of the Monte Carlo test with 1000 replicates are shown below. This
indicates that the amount of variability explained by the environmental variables is
significant for both the first and second canonical axes ( Probability < 0.05   less than
a 5% chance that the observed relationship could occur by chance)
The sample and species scores that will be plotted are presented in grids in the
Copyright 2004  PISCES Conservation Ltd





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