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Community Analysis Package

Rotate output

. Select yes or no by clicking on the radio buttons. If yes is selected

a PCA is performed on the final site coordinates . The default is yes as this will

usually produce the most suitable plot.

Maximum iterations

. You can change the number of iterations used by the

stress minimisation algorithm by using the mouse to move the slider bar. The

default is 200. While there is a relationship between the number of iterations and

the magnitude of the stress level achieved, in practice there is often little

advantage in selecting a higher iteration number. You may like to vary this

number to become satisfied that the minimum stress level possible has been

achieved.

Main MDS Page

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11.2

Sample coordinates

This string grid presents the final coordinates for each site (column). The site

identifier is given in the first column, in the second and third columns are listed

the coordinates of each site for the two dimensional solution. This is also the

model that is plotted (see above).

Columns to the right of column 3 will also be filled if you specified a maximum

number of dimensions above 2 (the default). In these columns are the

coordinates of each site calculated for the model with the maximum dimension

size selected. These are not available for plotting within CAP.

Values within this grid can be copied and pasted into other programs in the

normal Windows fashion.

Main MDS Page

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11.3

Stress

This grid shows the iteration history for a two dimensional non metric

multidimensional scaling. The first column gives the iteration number, the second

the stress value at this iteration and the third the step size used to move the site

positions.

If a maximum number of dimensions above 2 is selected then this grid also

tabulates the final stress value for models ranging from 1 dimensional to the

maximum dimension selected by the user (the default is 2). These data are also

available as a plot. These data can give an idea of the true dimensionality of the

data set as stress will reach a minimum value once the necessary number of

dimensions to fully express the distances between sites is reached. It gives an

impression the suitability of a two dimensional plot to show between site

relationships. If a two dimensional representation is satisfactory, then an increase

in dimension number will not greatly decrease stress.

Main MDS Page

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