Influence on study outcomes of an inpatient study by the behavior of the study staff (PINgPOng): study protocol for a randomized clinical trial. - Coenen, Martin; Bingel, Ulrike; Zunhammer, Matthias; Berdaguer, Maria Soledad; Fuhrmann, Christine; Fimmers, Rolf; Rengelshausen, Jens; Hartmann, Gunther; Schedlowski, Manfred; Coch, Christoph (Trials, 2022)