Quality of Life Assessment of Randomized Controlled Trials

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.

Comparison of construct validity of two short forms of Stroke-Specific Quality of Life scale

Background

No studies have compared the 2-factor structures of Wong’s and Post’s versions of the short-form Stroke-Specific Quality of Life (i.e., 12-item SSQOL) scale. This study compared the construct validity of 2 short-forms of the 12-item-SSQOL (not the 12-domain-SSQOL).

Methods

Data were obtained from a previous validation study of the original 49-item SSQOL in 263 patients. Construct validity was tested by confirmatory factor analysis (CFA) to examine whether the two-factor structure, including psychosocial and physical domains, was supported in both versions. The CFA tested the data-model fit by indices: chi-square χ²/df ratio, root mean square error of approximation (RMSEA), comparative fit index (CFI), nonnormative fit index (NNFI), standard root mean square residual (SRMR), and parsimony normed fit index (PNFI). Item factor loadings (cutoffs: .50) were examined. Model fit was compared using Akaike information criterion (AIC) and consistent AIC (i.e., CAIC) values.

Results

All model fit indices for Post’s version fell within expected ranges: χ²/df ratio = 2.02, RMSEA = 0.05, CFI = 0.97, NNFI = 0.97, SRMR = 0.06, and PNFI = 0.76. In the psychosocial domain, the item factor loadings ranged from 0.46 to 0.63. In the physical domain, all items (except the language and vision items) had acceptable factor loadings (0.68 to 0.88). However, in Wong’s version, none of the model indices met the criteria for good fit. In model fit comparisons, Post’s version had smaller AIC and CAIC values than did Wong’s version.

Conclusions

All fit indices supported Post’s version, but not Wong’s version. The construct validity of Post’s version with a 2-factor structure was confirmed, and this version of the 12-item SSQOL is recommended.