A statistical analysis of the seasonality in sudden infant death syndrome.

Sudden Infant Death Syndrome (SIDS) has a characteristic peak incidence in the winter months and a peak incidence at the age of two to four months. The present study examines whether the seasonality is related to the time of birth-the time of death or both. The data for the study relates to 116 cases of SIDS, representing 95% of all registered cases of SIDS in eastern Denmark in a three-year period 1981 to 1983. They were all autopsied at the Institute of Forensic Medicine in Copenhagen and evaluated by the same people. The framework of the analysis is a multiplicative Poisson-model with three sets of parameters describing the effects of the age of the infant, the time of death and the time of birth. The analysis proved the seasonality related alone to the time of death. An identical analysis was performed for 123 infants who in the period 1973-83 in eastern Denmark died from infectious diseases. In these cases no significant effect of the month of birth or the month of death was shown.