The Shoulder Disability Questionnaire differentiated well between high and low disability levels in patients in primary care, in a cross-sectional study

To investigate the usefulness of the Shoulder Disability Questionnaire (SDQ) for cross-sectional discriminative purposes, we assessed the discriminative ability of items, internal consistency, content validity, and construct validity. Two hundred patients recruited in primary and secondary care identified their chief functional limitations, scored their shoulder pain, and completed the SDQ. Two physical therapists assessed the range of motion, muscle force, and scored the severity of disability. Comparison of the chief functional limitations of the patients with the SDQ items confirmed the content validity of the SDQ. Cronbach's alpha describing the internal consistency was 0.79. Construct validity was confirmed for patients with different levels of pain, range of active abduction, muscle force, ability to perform activities in daily life, and the severity of disability scored by the physical therapists. However, the differences in the SDQ-score between extreme groups were less evident in the secondary care population. In patients in the secondary care rheumatology clinic, the discriminative ability of most SDQ items was very limited. The presented results suggest that the SDQ appears to be a useful discriminative instrument, especially in the primary care setting