Assessment of the impact of ambient air pollutants on health in Helsinki, Finland.

Several studies from various countries within the last decade have shown that ambient air pollutants cause short-term health effects in lower concentrations than believed earlier. Obtaining reliable and comprehensive health and environmental data is difficult but is the basic prerequisite for these studies. Linkage of data on air pollution and on several health effects has been conducted in Helsinki since the late 1980s, using time series analysis. The uniform population, small socioeconomic differences, a practically free national health care system with high coverage and extensive health, pollution and meteorological data render such studies possible. These kinds of local studies are necessary because many confounders or modifiers cause problems for the generalization of results of studies from other locations. Internal standardization, recommendations and guidelines concerning the methodology of linkage studies are needed to save work and money and to ensure the reliability of results.