1 Department of General Practice, Groningen Research Institute for Asthma and COPD, University Medical Center Groningen, University of Groningen, Groningen, 9713 AV, Netherlands; Unit of Pharmacoepidemiology & Pharmacoeconomics, Department of Pharmacy, University of Groningen, Groningen, Netherlands. Electronic address: j.f.m.van.boven@rug.nl.
2 Center for Pharmaceutical Outcomes Research, University of Colorado, Denver, USA.
3 Department of Academic Primary Care, University of Aberdeen, Scotland, UK; Observational and Pragmatic Research Institute, Singapore.