1 Department of Public Health and Primary Care, Leiden University Medical Center, PO Box 9600, 2300 RC Leiden, Netherlands. Electronic address: [email protected].
2 Department of General Practice, University of Maastricht, Research Institute CAPHRI, Maastricht, Netherlands.
3 Department of Pulmonary Diseases, Sint Franciscus Gasthuis, Rotterdam, Netherlands.
4 Department of General Practice and Groningen Research Institute for Asthma and COPD, University of Groningen, University Medical Center Groningen, Groningen, Netherlands.
5 Department of Public Health and Primary Care, Leiden University Medical Center, PO Box 9600, 2300 RC Leiden, Netherlands.