Scale agreement, ceiling and floor effects, construct validity, and relative efficiency of the PROPr and EQ-5D-3L in low back pain patients

BACKGROUND: The PROMIS Preference score (PROPr) is a new health state utility (HSU) score that aims to comprehensively incorporate the biopsychosocial model of health and apply favorable psychometric properties from the descriptive PROMIS system to HSU measurements. However, minimal evidence concerning comparisons to the EQ-5D-3L and the PROPr’s capability to differentiate clinical severity are available. Therefore, the aim of this study was to compare the PROPr to the EQ-5D-3L in terms of scale agreement, ceiling/floor effects, distribution, construct validity, discriminatory power, and relative efficiency (RE) in terms of the Oswestry Disability Index (ODI) for patients with low back pain (LBP). METHODS: We used intra-class correlation coefficients (ICC) and Bland–Altman plots to compare the PROPr and EQ-5D-3L with regared to scale agreement in a cross-sectional routine sample of LBP patients. For distribution, we used the Pearson’s coefficient for skewness and for ceiling/floor effects, a 15%-top/bottom threshold. For convergent validity, we used Pearson’s correlation coefficients. For known-groups validity, we applied a linear regression with interaction terms (predictors sex, age, and ODI level) and an analysis of variance (ANOVA). For discriminatory power, we calculated the effect size (ES) using Cohen’s d and the ratio of the area under the receiver-operating characteristics curves (AUROC-ratio = AUROC(PROPr)/AUROC(EQ-5D-3L)). RE was measured using the ratio of F-values (RE = F(PROPr)/F(EQ-5D-3L)). RESULTS: Of 218 LBP patients, 50.0% were female and the mean age was 61.8 years. The mean PROPr (0.20, 95%CI: 0.18; 0.22) and EQ-5D-3L scores (0.55, 95%CI: 0.51; 0.58) showed low agreement (d = 0.35, p < 0.001; ICC 0.27, 95%CI: -0.09; 0.59). The PROPr’s distribution was positively skewed, whereas the EQ-5D-3L’s was negative. Neither tool showed ceiling/floor effects, but all EQ-5D-3L dimensions did. Pearson correlation was r = 0.66 (95%CI: 0.58; 0.73). Differences were invariant to sex and age but not to ODI severity: ES(EQ-5D-3L) > ES(PROPr) and RE < 1 in higher ODI severity; ES(EQ-5D-3L) < ES(PROPr) and RE > 1 in lower ODI severity. AUROC-ratios did not show significant differences in terms of ODI severity. CONCLUSIONS: All PROPr and EQ-5D-3L biopsychosocial dimensions of health showed impairment in LPB patients. The capability of EQ-5D-3L and PROPr to differentiate ODI levels depends on ODI severity. Joint application of both tools may provide additional information.