Is association between mortality and air pollution due to a short temporal displacement?

Standard methodology for analysis of air pollution epidemiological time series expresses effects in terms of relative risk, i.e. increases in the number of events associated with a short term increase in air pollution. However, even large relative mortality rates may in fact reflect a very small effect in terms of person-years life loss. In Zagreb, mortality in 1995-1997 was significantly associated with concentrations of nitrogen dioxide (NO/sub 2/). We have used STL decomposition of time series into additive components of decreasing smoothness to test the hypothesis that mortality-air pollution association is due to short term mortality displacement. According to our results association between mortality and concentrations of NO/sub 2/ remains statistically significant at time scales ranging from a few days to 1-2 months.