Certain practical difficulties with clusters formed by the single-link method. For example, single-link clusters easily chain together and are often "straggly". Only a single edge between two large clusters is needed to merge the clusters. On the other hand, complete-link clusters are conservative. All pairs of objects must be related before the objects can form a complete-link cluster. Completeness is a much stronger property than connectedness. Perceived deficiencies in these two clustering methods have led to a large number of alternatives.