Modelling the relationship between the WOMAC osteoarthritis index and EQ-5D

Antonio Escobar Martinez,Allan Wailoo,Monica Hernandez Alava

doi:10.1186/1477-7525-12-37

Antonio Escobar Martinez, Allan Wailoo + Show 1 more

Open Access

https://doi.org/10.1186/1477-7525-12-37

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Abstract

ObjectiveEconomic evaluation typically is conducted using health state utilities to estimate treatment benefits. However, such outcomes are often missing from studies of clinical effectiveness. This study aims to bridge that gap by providing appropriate methods to link values from the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) to the EQ-5D utility instrument.MethodPatients from a large registry of Spanish patients (n = 7072 observations) with knee or hip osteoarthritis who completed both WOMAC and EQ-5D was used. A mixture model approach was used based on distributions bespoke to the EQ-5D UK value set to estimate EQ-5D as a function of WOMAC pain, stiffness and function subscores.ResultsA five class mixture model provides very close fit to the observed data at all levels of disease severity. The overall mean (0.542 vs 0.542), median (0.620 vs 0.636) and the percentage of observations at full health (15 vs 14.8) were very similar between the observed data and the estimated model respectively. Stiffness has limited relationship to EQ-5D, whereas functional disability and pain are strong predictors.ConclusionEQ-5D can be reliably estimated from WOMAC subscale scores without any systematic bias using these results.

Highlights

Osteoarthritis is one of the leading causes of pain and limitation in function, typically affecting the hip, knee and small hand joints
EQ-5D can be reliably estimated from WOMAC subscale scores without any systematic bias using these results
This paper reports on the application of such methods to modelling EQ-5D from WOMAC and other explanatory variables using data from patients with osteoarthritis of the hip or knee

Summary

Introduction

Osteoarthritis is one of the leading causes of pain and limitation in function, typically affecting the hip, knee and small hand joints. It is the most common form of arthritis and is characterised by extreme variability in clinical presentation, rate of disease progression and patient outcomes. One of the most widely reported outcome measures in Knee and Hip osteoarthritis is the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) [1]. With substantial evidence of psychometric validity it is in widespread use in clinical studies designed to assess the efficacy of technologies in this disease area. WOMAC is not a tool suitable for use in economic evaluation.

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