Investigating regional differences in short-term effects of air pollution on daily mortality in the APHEA project: A sensitivity analysis for controlling long-term trends and seasonality

Short-term effects of air pollution on daily mortality in eight western and five central-eastern European countries have been reported previously, as part of the APHEA project. One intriguing finding was that the effects were lower in central-eastern European cities. The analysis used sinusoidal ter ms for seasonal control and polynomial terms for meteorologic variables, bu t chi is a more rigid approach than the currently accepted method, which us es generalized additive models (GAM). We therefore reanalyzed the original data to examine the sensitivity of the results to the statistical model. Th e data were identical to those used in the earlier analyses. The outcome wa s the daily total number of deaths, and the pollutants analyzed were black smoke (BS) and sulfur dioxide (SO2). The analyses were restricted to days w ith pollutant concentration < 200 <mu>g/m(3) and < 150 <mu>g/m(3) alternate ly. We used Poisson regression in a GAM model, and combined individual city regression coefficients using fixed and random-effect models. An increase in BS by 50 mug/m(3) was associated with a 2.2% and 3.1% increase in mortal ity when analysis was restricted to days < 200 <mu>g/m(3) and < 150 <mu>g/m (3), respectively. The corresponding figures were 5.0% and 5.6% for a simil ar increase in SO2. These estimates are larger than the ones published prev iously: by 69% for BS and 55% for SO2. The increase occurred only in centra l-eastern European cities. The ratio of western to central-eastern cities f or estimates was reduced to 1.3 for BS (previously 4.8) and 2.6 for SO2 (pr eviously 4.4). We conclude that part of the heterogeneity in the estimates of air pollution effects between western and central-eastern cities reporte d in previous publications was caused by the statistical approach used and the inclusion of days with pollutant levels above 150 mug/m(3). However, th ese results must be investigated further.