| Research Abstract |
The investigation of disease clustering in space, in time or in both space and time is an important aspect of epidemiological studies to find clues to the causative mechanism of the disease in question. On this problem, the author proposed an index for disease clustering in time(1984, Biometrics 40, p15-26), which is applicable to grouped data with assumption that the population at risk remains fairly uniform over the study period. However, the asymptotic distribution of the index derived under the hypothesis of no clustering was rather complex for simple use and further it is not applicable to non-uniform case.
The present study (1) suggested a central chi square distribution as a better and simple approximation to the asymptotic distribution of the index, (2) allowed for non-uniform population distributions across the study period, and (3) extended the index so that it can be applied to space clustering problem where there are variations in distribution of the confounding factor such as age, sex.
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