Family conferences and shared prioritisation to improve patient safety in the frail elderly (COFRAIL): study protocol of a cluster randomised intervention trial in primary care oleh Achim Mortsiefer, Stefan Wilm, Sara Santos, Susanne Löscher, Anja Wollny, Eva Drewelow, Manuela Ritzke, Petra Thürmann, Nina-Kristin Mann, Gabriele Meyer, Jens Abraham, Andrea Icks, Joseph Montalbo, Birgitt Wiese, Attila Altiner, on behalf of the COFRAIL study group