1 Department of General Practice and Elderly Medicine, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands. Electronic address: h.van.der.worp@umcg.nl.
2 Department of General Practice and Elderly Medicine, University of Groningen, University Medical Center Groningen, Groningen, The Netherlands.
3 Julius Center for Health Sciences and Primary Care, University Medical Center Utrecht, Utrecht University, Utrecht, The Netherlands.
4 Department of Family Medicine, Care and Public Health Research Institute, Maastricht University, Maastricht, The Netherlands.