Content validity and psychometric properties of the inFLUenza Patient-Reported Outcome Plus (FLU-PRO Plus) instrument in patients with COVID-19

Document Type

Journal Article

Publication Date



Quality of life research : an international journal of quality of life aspects of treatment, care and rehabilitation




COVID-19; FLU-PRO Plus; Patient-reported outcome; Psychometric; Reliability; Validity


PURPOSE: A well-defined and reliable patient-reported outcome instrument for COVID-19 is important for assessing symptom severity and supporting research studies. The InFLUenza Patient-Reported Outcome (FLU-PRO) instrument has been expanded to include loss of taste and smell in the FLU-PRO Plus, to comprehensively cover COVID-19 symptoms. Our studies were designed to evaluate and validate the FLU-PRO Plus among patients with COVID-19. METHODS: Two studies were conducted: (1) a qualitative, non-interventional, cross-sectional study of patients with COVID-19 involving hybrid concept elicitation and cognitive debriefing interviews; (2) a psychometric evaluation of the measurement properties of FLU-PRO Plus, using data from COMET-ICE (COVID-19 Monoclonal antibody Efficacy Trial-Intent to Care Early). RESULTS: In the qualitative interviews (n = 30), all 34 items of the FLU-PRO Plus were considered relevant to COVID-19, and participants determined the questionnaire was easily understood, well written, and comprehensive. In the psychometric evaluation (n = 845), the internal consistency reliability of FLU-PRO Plus total score was 0.94, ranging from 0.71 to 0.90 for domain scores. Reproducibility (Day 20-21) was 0.83 for total score, with domain scores of 0.67-0.89. Confirmatory factor analysis with the novel smell/taste domain demonstrated an acceptable fit to the data. CONCLUSION: The content, reliability, validity, and responsiveness of the FLU-PRO Plus in the COVID-19 population were supported. Our results suggest that FLU-PRO Plus is a content- and psychometrically-valid, fit-for-purpose measure which is easily understood by patients. FLU-PRO Plus is a suitable PRO measure for evaluating symptoms of COVID-19 and treatment benefit directly from the patient perspective. TRIAL REGISTRATION: ClinicalTrials.Gov: NCT04545060, September 10, 2020; retrospectively registered.