1. Care and Public Health Research Institute, Department of Health Services Research, Maastricht University, Maastricht, The Netherlands
2. Institute of General Practice, Philipps-University, Marburg, Germany
3. FOM University of Applied Sciences, Siegen, Germany
4. University of Marburg, Marburg, Germany
5. Department of Medicine and Reflux Center Siegerland, Diakonie Hospital Jung Stilling, Siegen, Germany