The Stroke Impact Scale: validation in a UK setting and development of a SIS short form and SIS index.

BACKGROUND AND PURPOSE: The Stroke Impact Scale (SIS) covers 8 dimensions and a composite disability score. This study evaluates the SIS in the UK context, and develops a single index and an 8-item short form. METHODS: Patients with a diagnosis of stroke were recruited through general practices in London and the North-West of England. Patients completed the SIS and the EQ-5D. RESULTS: Internal consistency of the SIS dimensions and the disability score ranged from α 0.86 to 0.95. Complete data were available on 73 questionnaires (48.34%). Factor analysis suggested the 8 domains could be aggregated into a single index. A short-form SIS (SF-SIS) index was created by summing 1 item per dimension. Selected items were those that most highly correlated with their respective domain score (ρ ranged from 0.77-0.94, P<0.001). The SF-SIS index scores were highly correlated with those gained from the parent form (ρ=0.98; P<0.001). The correlation of the SIS index and SF-SIS index with the EQ-5D was identical (ρ=0.83; P<0.001). The disability score, whether scored from the dimensions of the SIS, or relevant items on the SF-SIS, were highly correlated (ρ=0.97; P<0.001). CONCLUSIONS: The SIS covers aspects of health, which are of importance to stroke patients, and the dimensions were found to have high levels of internal consistency in the UK context. The amount of incomplete data suggests that the length of the questionnaire may present a substantial patient burden. In comparison to the parent form the SF-SIS can accurately provide the disability score and overall index score with considerable brevity.