A comparison of preference assessment instruments used in a clinical trial: Responses to the visual analog scale from the EuroQol EQ-5D and the health utilities index

Objectives. To compare preference assessments that were made by using the E uroQol EQ-5D and the Health Utilities Index Mark II. Subjects. 561 patients in a randomized trial of tirilazad mesylate for aneurysmal subarachnoid he morrhage. Measures. Three preference assessments (a value score for the Eur oQol instrument and value and utility scores for the Health Utilities Index ) made three months after randomization. The averages for each of the three scores, stratified by clinical outcomes and attributes of the Health Utili ties Index health status classification system, were compared. To evaluate potential sources of difference between the instruments, the authors estima ted two alternative Health Utilities Index scoring rules that were based on patient responses to the EuroQol instrument. Results. Patients' ratings of their current health made by using the 100-point visual analog scale from the EuroQol instrument were more similar to the utility scores for the Heal th Utilities Index than they were to the value scores for the Health Utilit ies index. The biggest differences between the visual analog scores for the EuroQol instrument and the utility scores for the Health Utilities index w ere seen at higher levels of functioning. Conclusion. For states representi ng higher levels of functioning, differences were seen between patients' se lf-ratings obtained by using the EuroQol instrument and the patients' utili ty scores on the Health Utilities Index; for states representing lower leve ls of functioning, substantial agreement was observed between these two sco res. Differences observed at the higher levels of functioning suggest that further research is needed to determine whether the Health Utility Index's assignment of a score of 1.0 to the reference state representing being heal thy is appropriate.