Development, validity and reliability of the food allergy independent measure (FAIM)

Background: The Food Allergy Quality of Life Questionnaire-Child Form, -Teenager Form and -Adult Form (FAQLQ-CF, -TF and -AF) have recently been developed. To measure construct validity in the FAQLQs, a suitable independent measure was needed with which FAQLQ scores could be correlated. However, in food allergy, no appropriate independent measure existed, which could be used for this purpose. Aims of the study: The aim of this study was to describe the development of a Food Allergy Independent Measure Child-Form, -Teenager Form and -Adult Form (FAIM-CF, -TF and -AF) and to assess their validity and reliability. Methods: The FAIMs were developed using previously established methodology to capture the patients' expectation of outcome (EO). Face validity was determined by expert opinion. FAIM questions showing no correlation to any potential items in the FAQLQs were considered irrelevant and eliminated. To measure test-retest reliability, one-hundred and one patients were included and completed the FAIM twice with a 10-14 day interval. The intraclass correlation coefficient (ICC), Lin's concordance correlation coefficient (CCC) and Bland-Altman plots were used to assess test-retest reliability. Results: Six FAIM questions were developed and considered relevant for the FAIM-CF and -AF, and five questions were relevant for the FAIM-TF. The FAIMs showed good reliability with ICCs and CCCs above 0.70 and with mean differences all close to zero. Conclusions: Food allergy independent measures were developed for children, adolescents and adults and were shown to be valid, relevant and reliable. This supports the suitability of the FAIMs for evaluating construct validity.