Table 5 Key issues that limit modelling cost‐utility in ankylosing spondylitis and recommendations for future research.
Model issue | Present study | Limitation | Proposal | |||
---|---|---|---|---|---|---|
Definition of disease states that are clinically and economically relevant | BASDAI | • Limited in relating clinically and economically relevant disease states | • Combined (BADAI‐BASFI) outcome measures. Application in models would require data from large RCTs and cohorts | |||
• Patient perspective without external (objective) criterion | • New measure including external criterion | |||||
Number of disease states that are distinguished | BASDAI <4 opposed to ⩾4 | Limited number of disease states hampers identification of groups for which treatment is more or less cost‐effective | Determination of more disease states that are clinically (and economically) relevant. Application in models would require data from large RCTs | |||
Natural course of the disease | • 5 year time horizon | Reduced ability to show additional long term beneficial effects of TNFα inhibition. | Gain insight into progression of the disease and measures to capture the progression | |||
• After initial placebo response no change in BASDAI over 5 years | ||||||
Utilities | • Utilities measured in cohort | • Patients in the cohort did not experience the beneficial influence of the TNFα inhibitors | • Utilities derived directly from observational studies | |||
• EQ‐5D as only utility measure | • Different utilities can give different results | • Consensus of the recommended utility | ||||
Long term toxicity | From RCTs and open studies with low sample sizes and short observations | • Initial RCTs showed more toxicity than later RCTs | Long term observational studies | |||
• Limited long term observational data |
BASDAI, Bath ankylosing spondylitis disease activity index; BASFI, Bath ankylosing spondylitis functional index; EQ‐5D, EuroQol 5 dimensions utility index; RCT, randomised controlled trial.