Seasonal Variation of Infant Mortality Analyzed by Census Method

[摘要] Mortality of early infancy and children in Japan (converted into annual deaths against 1, 000 live births) is calculated month by month for 1961-67, with monthly deaths duely adjusted separately for early infants 0-1 year old and children 1-5 years old. Regarded as a time series, it is analyzed by the Census Method II X-11 (developed by the U.S. Census Bureau) for five age groups, i.e. early infants 0-1 year, and children 1-2 years, 2-3 years, 3-4 years and 4-5 years old. (Deaths of these age groups are collectively named infant mortality in this paper simply for sake of linguistic convenience.) It is thus found to show a seasonal variation peculiar to each age group.For early infants under 1 year, for instance, (1) mortality is considerably high in winter, (2) its seasonal variation is getting smaller as a whole, and (3) it begins to curve up in summer as well as in winter, though slightly. For other age groups, however, the seasonal pattern of mortality varies differently: (1) mortality is rather high from winter through summer for 1-2 years old, and (2) it is relatively low in winter for 2-5 years old.Then, with accidental deaths (mostly drowning) or the most frequent death cause for children omitted, infant mortality is recalculated and the time series thus adjusted is analyzed by the X-11 method for the five age groups. It is found that the seasonal variation shows little difference before and after adjustment (removal of accidental deaths) for early infants under 1 year, and that the "adjusted" variation for 1-2 years old curves up conspicuously in winter and slightly in summer, indicating the similarity in pattern and range between the first two age groups. For 2-5 years old, be it noted, the range of variation becomes tangibly smaller with short-cycle ups and downs, though somewhat peculiar changes are seen in pattern.It might well be concluded that infants under 2 years old are liable to suffer from seasonalchanges in both winter and summer, and that children 2-5 years old are well able to endure seasonal influences, winter cold and summer heat in particular.

[学科分类] 大气科学