1. Biometrics and Epidemiology, Institute of Medical Data Management, Ludwig-Maximilians-University, Munich, D-85758 Germany, Institute of Epidemiology, GSF National Research Center for Environment and Health, Efurt, D-99096 Germany, Institute for Inhalation Biology, GSF National Research Center for Environment and Health, Neuherberg/Munich, D-85758 Germany, and Institute for Tropospheric Research, Leipzig, D-04318 Germany