Abstract
This paper presents a biometeorological study in the seasonal variation, by regions of the United States, of motality from both stroke (Int. List No.330-334, vascular lesions affecting the central nervous system) and heart diseases (Int. List No.410-443). We intend in this study to investigate into the chronological process of reduction in seasonal variation of mortality witnessed in recent years in the United States. The crude death rate varies fairly widely from region to region, depending upon the age composition of population, living conditions, and so forth in each state. Thus, the United States is divided into eight regions on the basis of geographical features, climate and socio-economic conditions related to these natural environments, and an attempt is made to find out the trends of mortality from stroke and heart diseases in the three decades,1930's (1930-34),1940and 1950. The following four types of seasonal variation in mortality are found:
A) Nosummer peak is witnessed from the start in the mortality curve, bespeaking a fairly moderate seasonal variation. A decade later, mortality appears concentrated in winter, then the variation begins to reduce markedly. This trend is seen in the mortality curves for both diseases in three regions, namely the Pacific, Mountain and Great Lakes regions, and in the curve for heart diseases in Florida. Generally speaking, this trend is characteristic of the more prosperous areas of the United States.
B) In the 1930's, a small peak exists in summer, then it gets flat with the result that seasonal variation becomes greater. But it has been steadily slowing down. This trend is seen for both diseases in the Great Plains South and the South regions and for stroke in Florida.
C) No summer peak is seen from the start and seasonal variation is small, but it does not to indicate any sign of moderation, while the death rate rises along with the concentration of deaths in the cold season. This tendency is seen for both diseases in the Great Plains North region.
D) The mortality curve rises markedly only in winter, and seasoonal variation gets more moderate in spite of the steady climb of the death rate. This is seen for both diseases in the highly industrialized Northeast region.
It can thus been seen that the recent trends in the reduction of seasonal variation in mortality in the United States vary visibly, depending upon the geographical and socio-economic conditions. But steady progress has been made in each region, though in different degrees. In the northern part of the Great Plains North region which is the coldest area in the United States, be it noted, the seasoonal variation in infant mortality becomes markedly moderate, but this phenomenon is not apparent for stroke and heart diseases, indicating the importance of artificial climate for aged people.
