Validation of the Stroke Specific Quality of Life Scale (SS-QOL): test of reliability and validity of the Danish version (SS-QOL-DK)

OBJECTIVE: To test the reliability and validity of the Danish version of the Stroke Specific Quality of Life Scale version 2.0 (SS-QOL-DK), an instrument for evaluation of health-related quality of life. DESIGN: A correlational study. SETTING: A stroke unit that provides acute care and rehabilitation for stroke patients in Frederiksborg County, Denmark. SUBJECTS: One hundred and fifty-two stroke survivors participated; 24 of these performed test-retest. INTERVENTION: Questionnaires were sent out and returned by mail. A subsequent telephone interview assessed functional level and missing items. MAIN OUTCOME MEASURES: Test-retest was measured using Spearman's r, internal consistency was estimated using Cronbach's alpha, and evaluation of floor and ceiling values in proportion of minimum and maximum scores. Construct validity was assessed by comparing patients' scores on the SS-QOL-DK with those obtained by other test methods: Beck's Depression Index, the General Health Survey Short Form 36 (SF-36), the Barthel Index and the National Institutes of Health Stroke Scale, evaluating shared variance using coefficient of determination, r2. Comparing groups with known scores assessed known-group validity. Convergent and discriminant validity were assessed. RESULTS: Test-retest of SS-QOL-DK showed excellent stability, Spearman's r = 0.65-0.99. Internal consistency for all domains showed Cronbach's alpha = 0.81-0.94. Missing items rate was 1.0%. Most SS-QOL-DK domains showed moderately shared variance with similar domains of other test methods, r2 = 0.03-0.62. Groups with known differences showed statistically significant difference in scores. Item-to-scale correlation coefficients of 0.37-0.88 supported convergent validity. CONCLUSIONS: SS-QOL-DK is a reliable and valid instrument for measuring self-reported health-related quality of life on group level among people with mild to moderate stroke.