[1] Recognition of a cluster depends on its size being greater than would be expected by chance.
[1] Identification of a suspected disease cluster may initially depend on anecdotal evidence.
[1] Epidemiologists and biostatisticians then assess whether the suspected cluster corresponds to an actual increase of disease in the area.
[1] Typically, when clusters are recognized, they are reported to public health departments in the local area.
[citation needed] John Snow's pioneering investigation of the 1854 cholera outbreak in Soho, London, is seen as a classic example of the study of such a cluster.