Seasonal Variation of Infant Mortality Analyzed by Census Method (II)

Abstract

In their previous paper, the authors (1973a, 1973b) analyzed the seasonal variation of infant mortality during 1961-67 by the Census Method II X-11 and found that the death peak has tangibly declined in winter, whereas the summer hill has been getting relatively higher. In the present report, they want to present results of their new investigation: Is this phenomenon an omnipresent one in Japan or confined to some parts of the country?
The variation of the seasonal component of the death rate isolated by the X-11 method is considered as the real seasonal variation of infant mortality. It is thus found that during 1968-72 the death rate has got considerably moderate on the whole in all parts of the country, that such moderation has been particularly remarkable in highly urbanized regions, such as Tokyo, Aichi, Osaka, Hiroshima and Fukuoka, and that two peaks in winter and summer have become nearly equal to each other.
Such lowering of the winter upcurve appears to have come from the recent improvement of room heating in the cold months.
The relative prominence of the summer hill, however, cannot be explained so easily as the lowering of the winter summit. In recent years. mortality has visibly declined due to the development of medical science and technology, the marked improvement of living conditions and other favorable factors, but there still remains some causes for morbidity and mortality which cannot be eliminated completely, including some severe environmental elements like cold in winter and heat in summer. This is the very reason why deaths invariably increase in the cold and hot months.