Purpose
Graphically display the similarity between Sites (or something analogous) based on the presence or absence of items. Sites that share many of the same items and are missing many of the same items are expected to be very similar.
Analysis
The goal of the analysis is to produce a dendrogram.
Typical Data
Notes:
You can enter your data in several ways:
. Site_1 Site_2 Site_3 Site_4 Site_5
Item_1 1 1 0 1 0
Item_2 1 1 1 0 1
Item_3 1 1 0 0 0
Item_4 1 0 1 1 0
Item_5 0 1 1 1 0
Item_6 0 1 0 0 0
Item_7 1 1 1 1 1
Item_8 0 0 1 0 1
Generalizations
Dendrograms are used to show patterns. This type of analysis applies to many situations.
Example Problems (test your skills)
This diagram (generated from the "typical data" at the right) shows that the most similar sites are 3 and 5. The least similar site is 4.
Analysis Software
Use the PAST program. It is a free download (Windows PC only) and runs without the need for installation.
Start PAST and enable both of the Edit checkboxes (Edit Mode and Edit Labels).
Enter your data directly into the PAST spreadsheet or by cutting and pasting from another source (e.g., an Excel worksheet). You can also prepare a comma-delimited text file. (See information and examples on the right.) When you have completed your data entry, uncheck the Edit checkboxes.
You need to Transpose your data (rotate 90 degrees). Click on the Edit menu and choose the Transpose item.
After transposition, the area with your data values will already be selected. If you somehow deselect this area, you need to click-and-drag over the data area (not labels) to select it again before running an analysis.
Run the analysis by clicking on the Multivar menu and choosing the Cluster Analysis item. The analysis will run immediately and provide you with a dendrogram. However, you must choose the Bray-Curtis radio button to get the corrects display (Bray-Curtis assumes binary data as you are using).