Statistical analysis of geographical features of lung cancer mortality in Japan

Background: There is concern about the increase in death rates from lung ca ncer and that it may become the leading cause of death in the near future. Considerable geographical variations exist in lung cancer mortality in Japa n. It seems that the difference cannot be explained by smoking rates, altho ugh no data are available to prove this. The evidence implies some unknown risk factors in the development of lung cancer. As an alternative approach, we used geographical or demographic information according to municipality. To explore other factors in lung cancer development, the geographical feat ures of trends in lung cancer mortality in japan were examined using long-t erm data. Methods: We summarized the 20-year municipality-specific standardized morta lity ratios (SMRs) by fitting a straight line to the scatter plot of the SM R versus calendar year for each municipality, resulting in an average and a rate of change of SMR. Using the average or rate of change in the SMR as t he response variable, we carried out a multiple linear regression analysis for all of Japan and a non-parametric regression analysis for the distance from the municipal office to the nearest coastline, using the ACE algorithm . Results: The average SMR decreased with distance from the coastline and inc reased with increasing population size of the municipality. The average SMR was high at or near the coastline irrespective of the direction of the nea rest coastline. Conclusions: It was considered that something related to coastline other th an population size may be associated with the development of lung cancer.