1. Department of Pulmonary Diseases and Tuberculosis; University of Groningen, University Medical Center Groningen; Groningen Netherlands
2. Groningen Research Institute of Asthma and COPD (GRIAC); University of Groningen; Groningen Netherlands
3. Department of Epidemiology; University of Groningen, University Medical Center Groningen; Groningen Netherlands
4. Division of Respiratory Medicine; West Park Healthcare Centre, University of Toronto; Toronto Canada