Temporal and spatial relations between age specific mortality and ambient air quality in the United States: regression results for counties, 1960–97

Abstract

Objective: To investigate longitudinal and spatial relations between air pollution and age specific mortality for United States counties (except Alaska) from 1960 to the end of 1997. Methods: Cross sectional regressions for five specific periods using published data on mortality, air quality, demography, climate, socioeconomic status, lifestyle, and diet. Outcome measures are statistical relations between air quality and county mortalities by age group for all causes of death, other than AIDS and trauma. Results: A specific regression model was developed for each period and age group, using variables that were significant (p<0.05), not substantially collinear (variance inflation factor <2), and had the expected algebraic sign. Models were initially developed without the air pollution variables, which varied in spatial coverage. Residuals were then regressed in turn against current and previous air quality, and dose-response plots were constructed. The validity of this two stage procedure was shown by comparing a subset of results with those obtained with single stage models that included air quality (correlation=0.88). On the basis of attributable risks computed for overall mean concentrations, the strongest associations were found in the earlier periods, with attributable risks usually less than 5%. Stronger relations were found when mortality and air quality were measured in the same period and when the locations considered were limited to those of previous cohort studies (for PM 2.5 and SO 4 2- ). Thresholds were suggested at 100–130 μg/m 3 for mean total suspended particulate (TSP), 7–10 μg/m 3 for mean sulfate, 10–15 ppm for peak (95th percentile) CO, 20–40 ppb for mean SO 2. Contrary to expectations, associations were often stronger for the younger age groups (<65 y). Responses to PM, CO, and SO 2 declined over time; responses in elderly people to peak O 3 increased over time as did responses to NO 2 for the younger age groups. These results generally agreed with previous prospective cohort and ecological studies for comparable periods, age groups, and pollutants, but they also suggest that the results of those previous studies may no longer be applicable. Conclusions: Spatially derived relations between air quality and mortality vary significantly by age group and period and may be sensitive to the locations included in the analysis.

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Affiliated Institutions

• Northport VA Medical Center US

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