Agglomerative cluster analysis

77

15.8

Cluster groups

This grid gives the membership of each cluster arranged by rows. The first

column gives the cluster formation number   this is the cycle during which the

cluster was formed. The second column, termed the group label gives an

identifier for the cluster based on the membership. The group label is smallest

number of the column numbers of samples included within the group. Thus if

samples in columns 23 and 45 are joined to form a cluster the group label will be

23  If at some later point these samples are joined with the sample in column 1

then the group label for this new cluster will be 1. From column 3 onwards the

members of each cluster are given.

To print this output use File | Print.

15.9

Dendrogram   Cluster analysis

The dendrogram of the cluster relationships is shown by clicking on the

Dendrogram tab.

The dendrogram is drawn with green and blue nodes. These can be selected by

clicking on them with the mouse to obtain information about the clusters or

change the colour or organisation of the dendrogram as follows.

Sizing the dendrogram to either fit the screen or make the sample titles

readable

. The left hand button in the lower panel is a toggle which changes

between Fit Screen and Fit Text. When Fit Screen is active the dendrogram is

displayed  in a single window but for larger dendrograms the labels will overlap.

To see the labels clearly, select Fit Text and use the slider to move down the

dendrogram.

Changing the size of the font used for the labels

. Click on the Font button and

select font type and size.

Identifying the cluster group

. Click on the Cluster Id button in the lower panel

and move the cursor, which will be in the form of a question mark, to the node of

interest and click. The cluster group identification number will be shown. The

members of this cluster group can be found by referring to the Cluster groups

window (see above).

Changing the colour of a group of clustered samples for display or

emphasis

. Click on the Change colour button in the lower panel and move the

cursor which will be in the form of a pointing hand to the basal node of the branch

of interest and click. The colour of the selected branch will change. To select the

colour to be used click on change colour.

Reversing the order of samples in a branch of the dendrogram

. This option is

primarily intended for use with TWINSPAN dendrograms, but is still active for

cluster analysis although it may give poor results. Click on the Switch Pos button

and move the cursor, which will be in the form of circle with arrows, to the node of

interest and click.

See also 

Dendrogram plots

77

15.10 Cluster summary

This window presents a table of the sequence of cluster formation. The first

column, entitled Cluster, gives a sequential number to each cluster formed. The

group 1 and group 2 columns identify the groups which are united to form the

Copyright 2004, PISCES CONSERVATION LTD