The responsiveness of the Shoulder Disability Questionnaire

Abstract

Objective: To evaluate the responsiveness of the Shoulder Disability Questionnaire (SDQ).

Methods: The study was conducted within the framework of an observational study on shoulder disorders in primary care. After first presentation of their complaints to the general practitioner and after one and six months, participants completed the SDQ, a single question on functional status (FSQ), and an ordinal 11 point scale for the severity of pain (PSS). Responsiveness of the SDQ was evaluated compared with that of the FSQ and PSS, by calculating responsiveness ratios and by plotting receiver operating characteristic (ROC) curves. Recovery according to the patient was used as an external criterion for clinically relevant improvement (complete recovery or much improved on a six point Likert scale was denoted as clinically relevant improvement).

Results: A total of 349 consecutive patients with shoulder disorders were enrolled in the observational study. Response rates ranged between 96% and 89%. Responsiveness ratios were slightly higher for the PSS compared with the SDQ (2.53 versus 2.22 at one month, 2.24 versus 1.89 at six months). The area under the ROC curve was 0.84 for both the SDQ and the PSS, and 0.72 for the FSQ.

Conclusion: The results of this study confirm the responsiveness of the SDQ, making it a useful instrument to assess functional disability in longitudinal studies.

Figure 1

Receiver operator characteristic (ROC) curves for ΔSDQ (Shoulder Disability Questionnaire, ΔPSS (Pain Severity Scale) and ΔFSQ (Functional Status Question) at one month. True positive rate (sensitivity) and false positive rate (100-specificity) are for discriminating between patients reporting clinical improvement or clinical stability. Potential cut off points for the SDQ: ΔSDQ = 18.75: sensitivity 74%, specificity 77% (optimal trade off); ΔSDQ = 40: (mean change in clinically improved patients) sensitivity 46%, specificity 98%.