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Comparative Study
. 2010;28(6):477-87.
doi: 10.2165/11533010-000000000-00000.

Understanding the relationship between the EQ-5D, SF-6D, HAQ and disease activity in inflammatory arthritis

Roisin Adams  1 , Cathal Walsh, Douglas Veale, Barry Bresnihan, Oliver FitzGerald, Michael Barry
Affiliations
Comparative Study

Understanding the relationship between the EQ-5D, SF-6D, HAQ and disease activity in inflammatory arthritis

Roisin Adams et al. Pharmacoeconomics. 2010.

Abstract

Background: The growth of economic analyses and in particular cost-utility analyses (CUA), which use the QALY as a measure of outcome, has heightened the interest in the methodologies used to calculate the QALY. The EQ-5D has produced quite different utility values from that of the SF-6D. This article seeks to understand these differences using a cohort of patients with inflammatory arthritis.

Objective: To examine the relationship between the disease-specific measure, Health Assessment Questionnaire (HAQ) disability index (DI) and the preference-based measures, SF-6D, EQ-5D and European League Against Arthritis (EULAR) Disease Activity Score (DAS) in patients with rheumatoid arthritis (RA) and psoriatic arthritis (PsA).

Methods: Patients with RA and PsA (n = 504) attending a tertiary rheumatology referral centre completed the HAQ, SF-6D and the EQ-5D before starting biological therapy and again 12 months later. The SF-36 was converted into a utility using the preference-based SF-6D. Clinical outcomes such as the DAS, joint counts and laboratory measures were also recorded. We calculated single index utility scores from the preference-based instruments using UK population norms. We used regression analysis to derive a mapping function and calculated utility scores from the HAQDI and the DAS 28.

Results: The mean utility observed at baseline for RA was 0.43 for the EQ-5D and 0.54 for the SF-6D and for PsA was 0.49 for the EQ-5D and 0.57 for the SF-6D. The utility gain demonstrated by the EQ-5D was over twice that of the SF-6D. The EQ-5D scored 17% of the RA group as less than 0 (state defined as worse than death); 7% of this group remained less than 0 at follow-up. The distribution of the utility estimates was similar for both RA and PsA.

Conclusions: Our findings draw attention to the impact of states worse than death on the overall distribution for the EQ-5D derived utilities and how these impact on its use in practice. EQ-5D-derived QALY changes are over twice that of the SF-6D. The implication of this for decision makers is that cost-effectiveness evaluations for treatments in this disease class are likely to be very sensitive to the choice of utility measure.

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References

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