How is proximity defined?
The proximity between clusters A and B is measured as =
1. Nearest neighbor (single linkage)
... Minimum of all possible distances of the cases in cluster A and of the cases in cluster B.
2. Centroid clustering (other linkage)
... Distance between the centroids of clusters A and B.
3. Furthest neighbor (complete linkage)
... Maximum of all possible distances of the cases in cluster A and of the cases in cluster B.