How do scores on the EuroQol relate to scores on the SF-36 after stroke?

The EuroQol and Medical Outcome Survey 36-item short-form health survey (SF-36) questionnaires have both been validated for the assessment of health-related quality of life after stroke. However, the relationship between these instruments has not been studied after stroke. We therefore sought to compare the responses of a group of stroke patients to both instruments. 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 SF-36 instruments. We randomly selected one third of patients who had responded to the EuroQol for follow-up, again using the SF-36, and two thirds of patients who had responded to the SF-36 for follow-up, again using the EuroQol. We assessed the patients' mean score for each domain of the SF-36 categorized by their response to the corresponding EuroQol domain and the correlation between the domains of the 2 instruments. The domains for both instruments, which assessed physical functioning, social functioning, bodily pain, and overall health-related quality of life, correlated closely. The mental health domain of the SF-36 correlated only poorly with the psychological functioning domain of the EuroQol. Both the EuroQol and SF-36 measure broadly similar domains of health. The weak relationship between the assessments of mental health may reflect a difference in content or more fundamental problems with the validity or reliability of the items in one of the instruments with respect to this domain. This study has provided the first empirical qualitative evidence by which the data on the SF-36 after stroke may be interpreted.