Validity, internal consistency and self-rated change of the patient enablement instrument in patients with chronic musculoskeletal pain

Objective: Patient enablement reflects patient's understanding of and coping with illness. The aim of this study was to investigate the content validity, construct validity, internal consistency and selfrated change (SRC) of the Patient Enablement Instrument (PEI) in patients with whiplash-associated disorders, cervical radiculopathy and mixed chronic pain treated in different settings. Design: Psychometric analyses. Participants: Patients with disabling non-malignant chronic musculoskeletal pain. Methods: Participants answered questionnaires on disability (Neck Disability Index (NDI) or Functional Rating Index (FRI)), anxiety/depression (Hospital Anxiety and Depression Scale; HADS) and general health (EuroQol; EQ-5D). Content validity, construct validity (confirmatory factor analysis), internal consistency and cut-off for SRC were investigated for the PEI after treatment. The SRC value was the receiver operating characteristic (ROC) curve optimal cut-off point. Results: After treatment all items were completed by 516 patients (mean standard deviation (SD) age 45.1 years (SD 10.1), women 75% (n=385)). The 1-factor PEI model had approximate fit to the data. The internal consistency Cronbach's alpha was between 0.878 and 0.929 for the 3 groups. Correlations between the PEI and the NDI/FRI, HADS and EQ-5D were fair to good. The SRCROC for whiplash-associated disorders, cervical radiculopathy and mixed chronic pain groups was 5, 6 and 4 points in the PEI, respectively. Conclusion: The PEI showed fair content validity, construct validity and internal consistency. However, the scale needs further development to improve measurement of change