Introduction: Fatigue is an important fibromyalgia (FM) symptom, but existing measures of fatigue are unlikely to meet regulatory standards for clinical trial use. We describe the development and validation of the Daily Diary of Fatigue Symptoms—Fibromyalgia (DFS-Fibro), a 24-hour recall, patient-reported outcome (PRO) measure of fatigue in FM that is administered electronically (ePRO). Methods: There were 3 phases of work: 1) item generation based on concept elicitation interviews with FM patients, with clinical relevance confirmed by expert clinician review; 2) pilot testing/cognitive debriefing interviews with FM patients; and 3) psychometric validation using data from a methodology study with 145 FM patients. The measure was finalised based on both qualitative and quantitative findings. Results: Twenty-three items were generated in phase 1, some minor revisions were made following the pilot testing and cognitive debriefing (phase 2) but none were deleted. All patients found the measure easy to understand and use. Item reduction was conducted taking into account both the initial psychometric data and the earlier qualitative research, resulting in a final 5 item measure of the “symptom” of fatigue. The 5-item DFS-Fibro had very high internal consistency (alpha = 0.99), and strong test-re-test reliability (r > 0.84), convergent validity and known-groups validity. Conclusion: The DFS-Fibro has strong psychometric properties and strong face and content validity for the measurement of fatigue in FM.
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