Responsiveness and Interpretability of the Portuguese Version of the Quebec Back Pain Disability Scale in Patients With Chronic Low Back Pain

Improving functional capacity is a common goal when providing physiotherapy treatment to patients with chronic low back pain (CLBP). In a clinical setting, clinicians and researchers are often interested in measuring change in a patient’s condition as a result of an intervention or to distinguish individual differences in response to treatment. To address change accurately in health-related outcomes, such as functional disability, clinicians need measurement tools that show responsiveness and are able to detect minimal changes in performance over time.This change must be large enough to be considered a “real” change and precise enough to detect small but important clinical changes over time considered to be important by patients and/or clinicians.The concepts of “minimal detectable change” (MDC) and “minimal clinically important difference” (MCID) have been introduced to help clinicians and researchers in assessing and interpreting patient changes. The MDC has been defi ned as the minimal amount of change that can be considered above the threshold of error expected in the measurement, whereas the MCID has been defined as the smallest change in an outcome measure that is perceived as benefi cial by the patient and that would lead to a change in the patient’s management, assuming an absence of excessive side effects and costs. The Quebec Back Pain Disability Scale (QBPDS) is a well established functional self-report questionnaire to assess changes in function in patients with CLBP participating in rehabilitation programs. Several studies have evaluated its reliability and validity and have had good results. However, studies addressing its responsiveness are scarce, especially in samples of patients with CLBP, and there is little agreement in their fi ndings. In those studies the MDC was in the range 11.04 23 to 24.6 (95% confi dence interval [CI]: 19.9–32.4) 14 and the MCID was in the range from 5 9 to 8.5 points. Moreover, and in what concerns its interpretability, there are only a few studies that have considered the MCID in relation to the MDC. Therefore, the purpose of this study was to examine the responsiveness of the QBPDS Portuguese version (PT) and to determine the MCID, MDC, and the floor/ceiling effects, in patients with CLBP.