Psychometric properties of the short form of the Stroke Impact Scale in German-speaking stroke survivors

The short form of the Stroke Impact Scale (SF-SIS) consists of eight questions and provides an overall index of health-related quality of life after stroke. The goal of the study was the evaluation of construct validity, reliability and responsiveness of the SF-SIS for the use in German-speaking stroke patients in rehabilitation. The SF-SIS, the Stroke Impact Scale 2.0 (SIS 2.0), EQ-5D-5L, National Institutes of Health Stroke Scale (NIHSS) and de Morton Mobility Index were assessed in 150 inpatients after stroke, with a second measurement two weeks later for the analyses of responsiveness. In 55 participants, the test-retest-reliability was assessed one week after the first measurement. The study was designed following the recommendations of the COSMIN initiative. The correlations of the SF-SIS with the SIS 2.0 ([rho] = 0.90), as well as the EQ-5D-5L ([rho] = 0.79) were high, as expected. There was adequate discriminatory ability of the SF-SIS index between patients who were less and more severely affected by stroke, as assessed by the NIHSS. Exploratory factor analysis indicated a two-factor structure of the SF-SIS explaining 59.9% of the total variance, providing better model fit in the confirmatory factor analysis than the one-factorial structure. Analyses of test-retest-reliability showed an intraclass correlation coefficient of 0.88 (95% CI 0.75-0.94). Hypotheses concerning responsiveness were not confirmed due to lower correlations between the assessments change scores. Trial registration The study was registered at the German Clinical Trials Register. Trial registration number: DRKS00011933, date of registration: 07.04.2017