Validation of two short forms of Stroke Impact Scale: unidimensionality and reliability.

Purpose: We examined the unidimensionality and Rasch reliability of both Jenkinson's and MacIsaac's eight-item short versions of the Stroke Impact Scale (SF-SIS), a questionnaire for assessing overall health-related quality of life (HRQOL).

Methods: This study was a secondary data analysis in which 263 persons with stroke completed the SIS. The 263 persons, on average, had age of 60 years, mild stroke, and moderate disability of self-care. The unidimensionality of both versions was validated via testing of model fitting and principal component analysis (PCA) of residuals using the Rasch analysis to determine the Rasch reliability and measures.

Results: The eight items in both SF-SIS versions met the criteria of infit and outfit MNSQ (<1.4 and >0.6), indicating good data-model fit. The PCA showed that no dominant factors existed in the residuals of the items. The person reliability of Jenkinson's and MacIsaac's SF-SIS versions was 0.80 and 0.79, respectively. The Rasch measures (i.e., person measure in logits) ranged from -1.06 to 1.87 in Jenkinson's SF-SIS and -0.82 to 1.88 in MacIsaac's version.

Conclusions: The unidimensionality of both versions was supported. The Rasch measures of both appear valid for representing overall HRQOL levels. Both versions also showed acceptable reliability for research purposes.Implications for rehabilitationThe unidimensionality was justified for both versions (Jenkinson's and MacIsaac's eight-item short-versions of Stroke Impact Scale).The Rasch scores of both versions appear valid for representing overall health-related quality of life.Both versions showed acceptable reliability for research purposes, but not sufficiently reliable for clinical use.