Effectiveness and cost-effectiveness of a guided Internet- and mobile-based intervention for the indicated prevention of major depression in patients with chronic back pain - study protocol of the PROD-BP multicenter pragmatic RCT - Sander, L.; Paganini, S.; Lin, J.; Schlicker, S.; Ebert, D. D.; Buntrock, C.; BAUMEISTER, H. (Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), 2017)