Derivation and Validation of a Modified Short Form of the Stroke Impact Scale

Abstract

Background: The Stroke Impact Scale (SIS) is a stroke-specific, quality of life measure recommended for research and clinical practice. Completion rates are suboptimal and could relate to test burden. We derived and validated a short form SIS (SF-SIS). Methods and Results: We examined data from the Virtual International Stroke Trial Archive, generating derivation and validation populations. We derived an SF-SIS by selecting 1 item per domain of SIS, choosing items most highly correlated with total domain score. Our validation described agreement of SF-SIS with original SIS and the SIS-16 and correlation with Barthel Index, modified Rankin Scale, National Institutes of Health Stroke Scale, and Euro-QoL 5 dimensions visual analog scales. We assessed discriminative validity (associations between SF-SIS and factors known to influence outcome [age, physiological parameters, and comorbidity]). We assessed face validity and acceptability by sharing the SF-SIS with a focus group of stroke survivors and multidisciplinary stroke healthcare staff. From 5549 acute study patients (mean age 68.5 [SD 13] years, mean SIS 64 [SD 32]) and 332 rehabilitation patients (mean age 65.7 [SD 11] years, mean SIS 61 [SD 11]), we derived an 8-item SF-SIS that demonstrated good agreement with original SIS and good correlation with our chosen functional and quality of life measures (all ρ>0.70, P<0.0001). Significant associations were seen with our chosen predictors of stroke outcome in the acute group (P<0.0001). The focus group agreed with the choice of items for SF-SIS across 7 of 8 domains. Conclusions: Using multiple, complementary methods, we have derived an SF-SIS and demonstrated content, convergent, and discriminant validity. This shortened SIS should allow collection of robust quality of life data with less associated test burden.