Non Metric Multidimensional scaling

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11.4

MDS plots

This window can show three different plots that are each selected using the radio

buttons below the graph.

Plot samples

   This shows the plot of the final positions for the sites (columns)

for a four dimensional non metric multidimensional scaling. Note the layout of the

sample coordinates table. Where more than two dimensions are chosen for the

ordination the grid displays the values for each species/value combination on the

right hand side of the grid, Axis 1 (2D) & Axis 2 (2D), on the left hand side

represent the result of further processing to enable two axes to be plotted against

each other.

Stress vs iterations

   This shows the plot of the stress against iteration number

for a two dimensional non metric multidimensional scaling model. A successful

analysis should show an approximately asymptotic decline in stress with iteration

number.

Stress vs Dimension

  This shows the plot of the final stress value plotted

against the dimension of the model. The maximum dimension on the plot is the

maximum number of dimensions selected during setup. This plot 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 of 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.

Each plot can be printed using 

File | Print

 and can be exported in a number of

different 

file formats

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 using 

File|Export 

or the Export page of the Edit Chart

dialog box. The graph can also be 

zoomed and panned

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. The facility is

particularly useful to magnify part of the plot with a tight cluster of points. Site

names can be added or removed from the plot using the Show labels tick box.

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