Materials and Methods This study was a pragmatic, observational study approved by the local regional ethics committee (KEK-ZH-Nr: 2014-0533). Patients and therapists signed informed consent prior to study commencement.

Patient Recruitment and Allocation

Patients with LBP were recruited consecutively from a waiting list for musculoskeletal physical therapy at the Kantonsspital Winterthur, a public hospital in Switzerland. Patient recruitment was based on the clinical information reported on the referral sheet for physical therapy. Included patients were scheduled randomly to therapists who participated in this study. The first author (E.B.) met recruited patients prior to the intake session to screen for eligibility.

Participants

Patients with chronic LBP were included for participation. Inclusion criteria were: age between 18 and 65 years, history of LBP for more than 3 months, the primary pain area localized in the lumbar spine (T12 to buttocks), and being able to complete the questionnaires independently in the German language. Exclusion criteria were: pregnancy, rheumatic diseases, progressive neurological diseases, unstable cardiac or pulmonary conditions, red flag disorders such as cancer, fracture, infection or spinal cord compression/cauda equina syndrome, surgery during the last 3 months or planned surgery. Finally, patients with a diagnosed mental illness (based on DSM-5 criteria30) reported on their referral sheet for physical therapy were excluded, however patients who reported psychological factors remained eligible. Therapists were graduated physical therapists or physical therapist students doing an internship for 3 or 5 months at the hospital. The physical therapist students were in their fourth or fifth semester of an 8-semester bachelors of science degree program from 2 different universities in Switzerland. There were no exclusion criteria for therapists.