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. Methods and Results: We examined data from the Virtual International Stroke Trial Archive, generating derivation and validation populations. We derived a short form (SF-SIS) by selecting one 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, NIHSS, and EQ-5D visual analogue 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]; 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 QOL measures (all rho>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 7/8 domains. Conclusions: Using multiple, complementary methods we have derived a short form 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