Disease clustering in time.

Tango (1984, Biometrics 40, 15-26) proposed a clustering index for testing for clusters of disease in time. A test based on this clustering index was shown to compare favourably with other statistical tests. In this article we show that Pearson's X2 and its components perform well in testing for clusters of disease in time. The rth of these components identifies a departure from uniformity in moments up to the rth and so helps describe the alternative, if any, to uniformity.