An agglomerative clustering method proposed by Ward in 1963. The clustering criterion is based on the error sum of squares, E, which is defined as the sum of the squared distances of individuals from the centre of gravity of the cluster to which they have been assigned. Initially, E is 0, since every individual is in a cluster of its own. At each stage the link created is the one that makes the least increase to E.
Subjects: Psychology — Probability and Statistics.