OBJECTIVES: to increase the knowledge about the performance of the five-level version (5L) of the EuroQol EQ-5D quality of life instrument.

METHODS: participants (n=151) aged over 70 from REFORM (REducing Falls with Orthoses and a Multifaceted podiatry intervention) trial completed the 3L and 5L instruments. Both instruments were assessed in terms of feasibility, reliability, validity, and efficiency for trial design.

RESULTS: completeness was higher for the 5L (96.7%) than for the 3L (92.7%). The proportion of inconsistent responses between both instruments was 3.25%. Redistribution from 3L to 5L showed valid results. For the 5L, 67 unique health states were observed compared with 27 for the 3L. The ceiling effect was reduced from 11.2% (3L) to 6% (5L). The absolute informativity (1.58 for 5L versus 0.97 for 3L) and relative discriminatory power (0.68 for 5L versus 0.61 for 3L) improved with the 5L. Variance of the index scores was lower for the 5L (σ2=0.040) than 3L (σ2=0.056).

CONCLUSIONS: our study supported the feasibility and validity of both instruments. However the 5L reduces ceiling effect and improves discriminatory power. The 5L could allow for more efficient sample size estimation and help to ameliorate missing data problem in cost-effectiveness analysis.