Average Group Linkage:
The average group linkage is a method of calculating distance between clusters in hierarchical cluster analysis . The linkage function specifying the distance between two clusters is computed as the distance between the average values (the mean vectors or centroids ) of the two clusters.
Mathematically the linkage function - the distance between clusters and - is described by the following expressions:
and are two sets of objects (clusters);
and are the numbers of objects in clusters and respectively;
and are the mean vectors of the first and the second clusters, respectively;
is the distance between vectors and .