Psychometric properties of 3 patient-reported outcome measures for the assessment of shoulder disability after neck dissection

Patient-reported outcome measures evaluating shoulder disability after neck dissection have not been sufficiently validated. We assessed the psychometric properties of the Shoulder Disability Questionnaire (SDQ), Neck Dissection Impairment Index (NDII), and the Shoulder Pain and Disability Index (SPADI) in patients after neck dissection. One hundred seven patients completed the SDQ, NDII, and SPADI on 4 occasions over 6 months, and underwent physical examination. We assessed internal consistency, test-retest reliability, clinical and construct validity, and responsiveness to change. The possibility of combining the NDII and SPADI items into a single scale was explored by Rasch analysis. All questionnaires exhibited good reliability and validity. We were successful in fitting a Rasch model to the data. The results support the suitability of the SDQ, NDII, and the SPADI for use in neck dissection patients. Combining the SPADI and NDII in a single Rasch scale improves item difficulty distribution but reduces variability and discriminative ability