The aim was to develop a German questionnaire for self-assessment of shoulder function equivalent to the Constant-Score (CS). To evaluate the retest reliability, the CS questionnaire was completed twice within 1 week by 47 patients prior to shoulder surgery. For validation the CS was assessed by the physician after the second self-test. The medium selectivity of the CS questionnaire at hospital admission was 0.47, the medium item difficulty 0.40, the test-retest reliability 0.675 ( p=0.000), the internal consistency of the questionnaire 0.80, and of the physician's CS evaluation 0.85. Construct, content, and discriminative validity of the questionnaire could be demonstrated. A high correlation of the patient-based questionnaire with the physician-assessed CS was found ( p=0.82). The statistical analyses demonstrated that the CS questionnaire is a reliable and valid instrument to evaluate the CS and can therefore be used for follow-up studies.

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