An analysis of the complementarity of ICECAP-A and EQ-5D-3L in an adult population of patients with knee pain

Background: The ICECAP measures potentially offer a broader assessment of quality of life and well-being, in comparison to measures routinely used in economic evaluation, such as the EQ-5D-3L. This broader assessment may allow measurement of the full effects of an intervention or treatment. Previous research has indicated that the ICECAP-O (for older people) and EQ-5D-3L measure provide complementary information. This paper aims to determine similar information for the ICECAP-A (for the entire adult population) in terms of whether the measure is a substitute or complement to the EQ-5D-3L. Methods: Data from the BEEP trial - a multi-centre, pragmatic, randomised controlled trial - were used. Spearman rank correlations and exploratory factor analytic methods were used to assess whether ICECAP-A and EQ-5D-3L are measuring the same, or different, constructs. Results: A correlation of 0.49 (p<0.01) was found between the ICECAP-A tariff score and the EQ-5D-3L index. Using the pooled items of the EQ-5D-3L and the ICECAP-A a two factor solution was optimal, with the majority of EQ-5D-3L items loading onto one factor and the majority of ICECAP-A items onto another. Conclusion: The results presented in this paper indicate that ICECAP-A and EQ-5D-3L are measuring two different constructs and provide largely different, complementary information. Results showed a similarity to results presented by Davis et al using the ICECAP-O.