| Abstract: | In many epidemiologic studies the first indication of an environmental or genetic contribution to the risk of disease is the way in which the diseased cases cluster within the same family units. The concept of clustering is contrasted with incidence. We assume that all individuals within the same family are independent, up to their disease status. This assumption is used to provide an exact test of the initial hypothesis of no familial link with the disease, conditional on the number of diseased cases and the sizes of the various family units. Ascertainment bias is described and the appropriate sampling distribution is demonstrated. Two numerical examples with published data illustrate these methods. |
