Psychometric parameters of food allergy quality of life during an allergen immunotherapy trial

Background The Food Allergy Quality of Life Questionnaire–Parent Form (FAQLQ‐PF) is a commonly used patient‐reported outcome measure in food allergy (FA) research. It was developed before FA treatment clinical trials were commonplace and is used as a secondary outcome measure in pivotal FA treatment trials. We examined the psychometric properties of the FAQLQ‐PF and its relevance to children with peanut allergy engaged in an epicutaneous immunotherapy (EPIT) clinical trial. Methods Analysis was performed on 26 universally answered items of the FAQLQ‐PF, from assessments undertaken during the phase 3 PEPITES study (baseline, Month 12), which examined the safety and efficacy of EPIT for children with peanut allergy aged 4–11 years. Item response theory (IRT) was used to assess psychometric parameters of the FAQLQ‐PF (i.e., discrimination, difficulty, and information). Confirmatory factor analysis was also employed; reliability was assessed using McDonald's omega (ω) and Cronbach's alpha (α). Results A total of 23 of 26 items presented very high discrimination levels (>1.7), and all 26 fell within the recommended difficulty threshold (between −1.5 and 1.5). The items contributed a reasonable information level for their respective factors/subdomains. The measure also presented a marginally acceptable model fit for the 3‐factor structure (e.g., comparative fit index = 0.88, Tucker–Lewis index = 0.87) and good reliability levels across time points (ω and α > 0.90). Conclusions Herein, we present a novel reanalysis of the FAQLQ‐PF items using IRT. The longitudinal performance of individual items and subscales was corroborated, and items with the highest discrimination were identified, showing that the tool is suitable for longitudinal measurements in FA treatment trials. We examined the item parameters of the FAQLQ‐Parental form, using a sample of parents of children engaged in an EPIT clinical trial. A total of 23 of 26 items presented very high discrimination levels; 25 fell within the recommended difficulty threshold; and all 26 items were associated with reasonable information level. The tool is suitable for longitudinal measurements in food allergy treatment trials.