Interrater reliability and construct validity of the Posture and Postural Ability Scale in adults with cerebral palsy in supine, prone, sitting and standing positions

Abstract

Objective: To evaluate reliability, internal consistency and construct validity of the Posture and Postural Ability Scale for adults with cerebral palsy. Design: Psychometric evaluation of a clinical assessment tool. Setting: Rehabilitation centres in Sweden and Iceland. Subjects: Thirty adults with cerebral palsy aged 19–22 years, six people at each level I–V of the Gross Motor Function Classification System. Main measures: The Posture and Postural Ability Scale contains a 7-point ordinal scale for postural ability in supine, prone, sitting and standing, and items for assessment of posture. Posture and postural ability was rated from photos and videos by three independent assessors. Interrater reliability was calculated using weighted kappa. Internal consistency was analysed with Cronbach’s alpha if item deleted and corrected item–total correlation. Construct validity was evaluated based on known groups, using Jonckheere Terpstra for averaged values of the three raters relative to the Gross Motor Function Classification System. Results: There was an excellent interrater reliability (kappa = 0.85–0.99) and a high internal consistency (alpha = 0.96–0.97, item–total correlation = 0.60–0.91). Median values differed (P < 0.02) between known groups represented by the levels of gross motor function, showing construct validity for all items. Conclusion: The Posture and Postural Ability Scale showed an excellent interrater reliability for experienced raters, a high internal consistency and construct validity. It can detect postural asymmetries in adults with cerebral palsy at all levels of gross motor function.