A linkage function is an essential prerequisite for hierarchical cluster analysis . Its value is a measure of the "distance" between two groups of objects (i.e. between two clusters).
Algorithms for hierarchical clustering normally differ by the linkage function used. The most common type of linkage functions give rise to the following algorithms for cluster analysis:
- Single linkage clustering ;
- Complete linkage clustering ;
- Average linkage clustering ;
- Average group linkage ;
- Ward´s linkage .