A Nationwide Health Risk Assessment of PM2.5 Exposure by Examining the Regional Concentrations-Response Relations in a Population-Based Epidemiological Study in Japan

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During the second year of the project (FY2022), we developed analytical methods to estimate the short-term associations between PM2.5 and mortality in Japan. To quantify these associations, we conducted a two-stage analysis. In the first stage, the location-specific risks of PM2.5 were estimated by utilizing a time-series quasi-Poisson model. We applied a distributed lag non-linear model along with a flexible functional form of splines to evaluate the location-specific associations. We controlled various important covariates, including weather variables, day of the week, and seasonal and long-term time trends. Sensitivity analyses were carried out to determine the robustness of our findings. To assess and compare the shapes of the concentration-response (CR) relationship, all local CR functions were formulated using a unified statistical design. In the second stage, we used a random-effect meta-analysis to combine the regional and national overall estimates.