The Pain Belief Screening Instrument (PBSI): Predictive validity for disability status in persistent musculoskeletal pain

Purpose. To evaluate the predictive validity of a screening instrument measuring disability, self-efficacy, fear of movement and catastrophizing, for disability status in patients with musculoskeletal pain in primary health care physical therapy. Development over time of pain-related disability, pain intensity, self-reported work capacity and overall daily function for subgroups of patients was also investigated. Method. Prospective and correlational study, where patients (n=168) with a pain-duration of 4 weeks or more completed the questionnaires and their cases were followed for 8 months to assess the variables of interest. For predictive validity of the screening instrument discriminant analyses were conducted. The development over time for subgroups was analysed by comparing scores at the first and second measurement. Results. The PBSI correctly classified 72% of the subjects as High-disabled (n=33) or Low-disabled (n=110), as measured with the Pain Disability Index (Wilks' lambda=0.848, p<0.005). For pain intensity, self-reported changes in work capacity and overall daily function the discriminant analyses were not significant. The High-disability group had increased disability, unchanged pain intensity and decreased work capacity and daily function after 8 months. Conclusion. The predictive validity of the PBSI for disability was confirmed. In clinical use the PBSI could serve as a mean to obtain supplementary and clinically useful information.