Well informed physician-patient communication in consultations on back pain – study protocol of the cluster randomized GAP trial - Voigt-Radloff, Sebastian; Schöpf, Andrea C.; Boeker, Martin; Frank, Luca; Farin, Erik; Kaier, Klaus; Körner, Mirjam; Wollmann, Katharina; Lang, Britta; Meerpohl, Joerg J.; Möhler, Ralph; Niebling, Wilhelm; et al. (Friedrich-Alexander-Universität Erlangen-Nürnberg, 2019)