Non Metric Multidimensional scaling

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11.1

Starting Configuration   MDS

Initial Start Position

This is a radio button selection. Select PCA to use a Principal Coordinates

Analysis to calculate the starting coordinates of the sites (columns). Select

random to use a random number generator to assign initial coordinates. The

default is to use a PCA. The algorithm used by CAP to find the final coordinates

will produce different results depending upon the starting configuration. Indeed, a

poor initial choice may result in the algorithm becoming trapped before a low

stress value is reached. Generally, PCA will produce a satisfactory choice. It is

often useful to undertake a few runs with random starting points to satisfy yourself

that the algorithm is finding a minimum stress solution.

Number of dimensions

. This is a slider bar activated by the mouse. The default

value is 2. If a higher number is chosen, the program will calculate the

configuration of the points from this dimension down to 1 dimension, list the final

stress for each number of dimensions under the Stress tab and display the

change in the stress value with number of dimensions graphically. The

coordinates of the points for the maximum number of dimensions is displayed

under the Sample coordinates tab. However, the plot of the positions of the site is

that found for a two dimensional space.

Similarity/Dissimilarity measure

. The measure to use is selected by clicking on

the radio button. A number of different measures can be used to calculate the

distances between sites. The options available are Euclidean distance, Sorensen

, Jaccard and simple matching similarity. The default is Sorensen s

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