Sensitivity analysis of EQ-5D-3L index scores in terms of discriminative and known-groups validity in SLE: introducing Adequate Health State.

OBJECTIVES: To investigate the ability of different EQ-5D-3L index scores to discriminate between verum drug and placebo (discriminant validity) as well as between responders and non-responders (known-groups validity) in the SLE patient population of two phase III clinical trials of belimumab.

METHODS: Data from the BLISS-52 (NCT00424476) and BLISS-76 (NCT00410384) trials (N = 1684), which both showed superiority of belimumab to placebo, were utilised. Responders were defined as SLE Responder Index 4 (SRI-4) achievers at week 52. The Pearson's χ2 and Mann-Whitney U tests were used for comparisons, and logistic regression analysis was used for adjustments for confounders and assessment of independence.

RESULTS: While full health state (FHS; EQ-5D index score 1) showed the best ability to discriminate between belimumab and placebo (adjusted OR: 1.47; 95% CI: 1.11-1.96; P = 0.008) and between SRI-4 responders and non-responders (adjusted OR: 3.47; 95% CI: 1.29-10.98; P = 0.020), the discriminative ability of EQ-5D index scores 0.800 or more reached statistical significance for both discriminant validity (adjusted OR: 1.29; 95% CI: 1.02-1.63; P = 0.036) and known-groups validity (adjusted OR: 3.08; 95% CI: 1.16-9.69; P = 0.034).

CONCLUSION: Overall, higher EQ-5D index scores were associated with increasing ability to discriminate between belimumab and placebo, and between responders and non-responders. EQ-5D index scores less stringent than FHS may be clinically relevant HRQoL goals of treatment in patients with SLE, introducing the concept of EQ-5D adequate health state when FHS is not achievable.