Abstract
In many fields, decision-makers give great weight to clusters of events. Public Health investigators look for common causal factors to explain clusters of cancer cases or birth defects. Molecular biologists look for palindrome clusters in DNA for clues to the origin of replication of viruses. Telecommunications engineers design capacity to accommodate clusters of calls being simultaneously dialed to a switchboard. Quality control experts investigate clusters of defectives. The probabilities of different types of clusters under various conditions are tools of the physical, natural, and social sciences.