Analysis of the occurrence of anencephalic stillbirths in the Fylde Peninsula, 1956--1967.

Computer-based statistical signal methods have been applied to the analysis of case-occurrence time and location data from a 12-year complete series of anencephalic stillbirths in the Fylde peninsula of Lancashire. In the absence of any certainty about causative or contributory factors in these occurrences, the primary questions are if the underlying process is Poisson, or if there is evidence of a seasonal influence, and if any regional differences or communicable factors can be identified. With the limited case numbers (124) most small-sample statistical tests were not sufficiently informative. But using pattern and print-process analysis methods and simulation techniques, further elucidation is possible; for example, it is shown that a seasonally rate-modulated Poisson process is a reasonable model for case occurrences in the southern region, but not in the north, for which a different process must apply and where some evidence exists of clustering of preferred inter-event intervals. It is concluded in particular, that there is a regional dependence, with seasonal factors, of the process underlying case occurrences, and in general, that signal analysis methods are useful in the interpretation of small-sample spatio-tempered epidemiological data.