The objective of this study was to develop a new PRO instrument to measure fatigue in SLE that addresses the conceptual limitations of existing PRO instruments. Here we describe the formulation, refinement and first evaluations of this new instrument, the FATIGUE-PRO.
Abstract
Objectives
This study aimed to implement a patient-centred and evidence-based approach to develop a novel patient-reported outcome (PRO) instrument to measure fatigue in patients with SLE.
Methods
A three-step mixed methods psychometric (MMP) approach was followed. Steps comprised first draft item generation and review using interview data; evaluation and refinement of second draft items using mixed methods data, including interview and quantitative data from a phase 2 clinical study in SLE analysed using Rasch Measurement Theory (RMT) analysis; and evaluation of the final FATIGUE-PRO items using RMT and complementary Classical Test Theory (CTT) analyses. Guided by MMP criteria, a team of clinicians and outcome-measurement experts assessed evidence to inform instrument development.
Results
Step 1 culminated in 55 items (n = 39 patients interviewed). Their refinement in step 2 using mixed methods evidence led to the final FATIGUE-PRO instrument comprising 31 items across three scales of fatigue: physical fatigue (9 items), mental and cognitive fatigue (11 items) and susceptibility to fatigue (11 items). Qualitative (n = 43 patients) and quantitative (n = 106 patients) evidence strongly supported the scales’ content comprehensiveness and targeting, item quality and fit, conceptual uniqueness and appropriateness of the response scale. The FATIGUE-PRO further benefited from excellent reliability (RMT: 0.92–0.94 and CTT: 0.95–0.96) and supportive evidence of construct validity from assessments against other PROs.
Conclusion
The conceptual advances, comprehensive coverage and strong psychometric properties of the FATIGUE-PRO will significantly advance the measurement and management of fatigue in SLE, both in clinical trials and routine practice.
Morel, T., Cano, S., Bartlett, S. J., Gordon, C., Haier, B., Regnault, A., … & Cleanthous, S. (2022). The FATIGUE-PRO: a new patient-reported outcome instrument to quantify fatigue in patients affected by systemic lupus erythematosus. Rheumatology, 61(8), 3329-3340.
