Identifying the primary outcome for a randomised controlled trial in rheumatoid arthritis: the role of a discrete choice experiment

Abstract

Objectives: the objective of this study was to establish the preferences of patients with Rheumatoid Arthritis (RA) about the best outcome measure for a health and fitness intervention randomised controlled trial (RCT). The results of this study were used to inform the choice of the trial primary and secondary outcome measure.

Methods: a discrete choice experiment (DCE) was used to assess patients’ preferences regarding a number of outcomes: foot and ankle pain, fatigue, mobility, ability to perform activities of daily living, and choice of footwear. Preferences were also gathered for different schedules and frequency of delivery for the health and fitness intervention. The initial outcomes were chosen based on literature review, clinician recommendation and patients’ focus groups findings. The DCE was constructed using the D-efficiency criteria with SAS software macros. The DCE compared hypothetical scenarios with varying levels of outcomes severity as well as the schedule of the intervention. Preference weights were estimated using a number of econometric models (conditional logit, mixed logit and generalized multinomial logit) which are based on different assumptions, to account for preference and scale heterogeneity. The attribute importance was established by using the partial log-likelihood method.

Results: 100 patients with RA completed 18 choice sets via a web based platform. Overall, patients selected foot and ankle pain as the most important outcome, with mobility being nearly as important. There was no evidence of differential preference between intervention schedules or frequency of delivery.

Conclusions: foot and ankle pain can be considered the patient choice for primary outcome of an RCT relating to a health and fitness intervention. This study demonstrated that, by using the DCE method, it is possible to incorporate patients’ preferences at the design stage of a RCT. This approach ensures patient involvement at early stages of health care design.

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Identifiers

ORCID for Lindsey Cherry: orcid.org/0000-0002-3165-1004

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