1. Institute of Medical Biometry and Statistics, Faculty of Medicine and Medical Center University of Freiburg Freiburg Germany
2. Evidence Synthesis Method Team, Department of Primary Education University of Ioannina School of Education Ioannina Greece
3. Institute of Social and Preventive Medicine University of Bern Bern Switzerland
4. Department of Statistics London School of Economics and Political Science London UK
5. Faculté de Médecine Université Paris Descartes Paris France