The content and construct validity of the modified patient specific functional scale (PSFS 2.0) in individuals with neck pain

Abstract

ABSTRACTStudy design: Clinical measurement study.Background: The Patient Specific Functional Scale (PSFS) is a commonly used outcome measure, however answering options differ and content validity has yet to be assessed.Objective: To assess the content validity of the PSFS in patients with neck pain presenting to a physical therapist. And secondly, to assess the construct validity of the PSFS using the preferred version identified in the content validity study.Methods: The target population consisted of patients with neck pain presenting to physical therapy. First, content validity was assessed through semi structured interviews and content thematic analysis. Second, construct validity was assessed on the PSFS 2.0 by examining its correlation with the Neck Disability Index (NDI).Results: Eleven patients were interviewed. Patients indicated the concept of ‘activity limitations’ is very important to them. The PSFS is considered to be relevant and easy to understand. Patients had an explicit preference for the PSFS 2.0 version (using a different answering option and example list) and indicated they preferred to answer the PSFS 2.0 together with a clinician. One hundred patients participated in the construct validity study on the PSFS 2.0. The median PSFS 2.0 score was 4.5 and the correlation with the NDI was substantial (0.54).Conclusion: The results of this study indicate that in individuals with neck pain, the PSFS is appropriate however; PSFS 2.0 is the preferred version. The PSFS 2.0 is considered to be valid in terms of content validity and construct validity for patients with neck pain.