A simple test for the aggregation of disease occurrence in genealogical data

A simple test for the aggregation of occurrence of a trait in genealogical data is given; a test criterion is developed, and the power of the test to detect aggregation of risk is computed. The test utilizes pairs of individuals between whom transmission of risk factors may occur. As long as aggregation is reasonably strong and prevalence not too low, only modest amounts of data are required. It provides an easy and inexpensive first examination of data which can reveal whether the effort required to conduct more elaborate genealogical studies and analysis is warranted.