Hierarchical single- and average-linkage clustering results, scored against random assignment to clusters of uniform size (solid symbols), and random assignment to clusters of the same size as the clades obtained by hierarchical clustering (open symbols). For single linkage (circles), the difference is strongest, reflecting the strong tendency of that algorithm to produce nonuniformly sized clusters (indicated by the negative scores of the solid circles) that do not contain any functional information (evidenced by the open circles, which show that even taking account for the cluster sizes produced, the score is equivalent to random assignment). The scores for complete linkage show little difference (open and solid diamonds are almost on top of each other), indicating that the cluster sizes returned by this algorithm are indicative of actual clusters in the data. Average linkage occupies the middle ground (triangles).
