Background and purpose: The reliability of the EuroQol and SF-36 questionnaires after stroke is not known. We therefore aimed to assess and compare the test-retest reliability of both instruments in a group of stroke patients.
Methods: A total of 2253 patients with stroke entered by United Kingdom hospitals in the International Stroke Trial were randomized to follow up with either the EuroQol or the SF-36 instruments. For both instruments, we randomly selected one third of respondents and asked them to complete another, identical questionnaire. We assessed test-retest reliability using agreement statistics: unweighted kappa statistics for the categorical domains of the EuroQol and intraclass correlation coefficients for the EuroQol visual analog scale, utility scores, and SF-36.
Results: For the five categorical domains of the EuroQol, reproducibility was generally good (kappa ranged from 0.63 to 0.80). The reproducibility of the domains of the SF-36 was qualitatively similar for all the domains except mental health (intraclass correlation coefficient=.28). However, the 95% confidence intervals for the difference in scores between test and retest were substantial. For both instruments, reproducibility was better when the patient completed the questionnaires than when a proxy did.
Conclusions: Both the EuroQol and SF-36 have acceptable and qualitatively similar test-retest reliability. Therefore, either instrument might function effectively as a discriminatory measure for assessing health-related quality-of-life outcomes in groups of patients after stroke. However, our data do not support the use of either instrument for serial assessments in individual patients unless very large differences over time are expected.