The Interpretability of Change Scores of the Pain Disability Index and its Responsiveness in Chronic Musculoskeletal Pain Rehabilitation

Purpose:The Pain Disability Index (PDI) questionnaire assesses the reduction of disability, the main goal of chronic musculoskeletal pain (CMSP) rehabilitation.Moreover, the PDI is widely used and its clinimetric properties seem to be positive.This study aimed to provide reference values to interpret change scores of individuals on the PDI, for daily clinical practice, and to assess its responsiveness. Methods:The smallest detectable change (SDC), and minimal clinically important change (MCIC) of the PDI were investigated in 374 patients with CMSP, participating in an interdisciplinary pain rehabilitation programme (IPRP).Two Global Perceived Effect (GPE) statements were used to investigate these properties and values. Results:The hypotheses concerning correlations of the GPEs with the change scores on the PDI could not be confirmed.The SDC was evidently larger than the MCIC, independent of the GPE used. Conclusion:The PDI appeared not to be able to distinguish clinically important change from measurement error in individual patients for a broad range of change scores.For now, the calculated SDC can be used as a cut-off score to be fairly certain of real improvement.Further research is necessary to enhance usability.