Study of cancer mortality by grid square method.

The grid square method as used in Japan has been standardized by the government, by use of the lines of the earth's latitude and longitude. The basic unit covers an area of approximately one square kilometer. An evaluation of this method is focused on the geographical distribution of cancer mortality in the city of Tokyo over a period of six years. The results indicated that for stomach and lung cancers, there was a very clear geographical distribution. High stomach cancer areas were similar for both males and females, and by comparing data with census data, it was evident that the blue-collar areas showed high mortality. High lung cancer areas were also similar for both males and females, but the distribution was opposite to that of stomach cancer, i.e., the higher mortality was observed in white-collar areas. Because the basic area unit of one square kilometer was too small for statistical analysis of geographical distribution, the moving average of nine grid squares as well as a "combined grid square method" based on population density was used. By this study a number of advantages of the grid square method as opposed to methods employing existing government boundaries became evident. The boundary lines do not move with political expediencies. X-Y coordinates can be easily defined for statistical analyses by computer, facilitating computer mapping, calculating the center of distribution, determination of the contour lines, and the estimation of values in places which lie between sampling stations.