Development, validation and item reduction of a food literacy questionnaire (IFLQ-19) with Australian adults

BACKGROUND: Food literacy is theorised to improve diet quality, nutrition behaviours, social connectedness and food security. The definition and conceptualisation by Vidgen & Gallegos, consisting of 11 theoretical components within the four domains of planning and managing, selecting, preparing and eating, is currently the most highly cited framework. However, a valid and reliable questionnaire is needed to comprehensively measure this conceptualisation. Therefore, this study draws on existing item pools to develop a comprehensive food literacy questionnaire using item response theory. METHODS: Five hundred Australian adults were recruited in Study 1 to refine a food literacy item pool using principal component analysis (PCA) and item response theory (IRT) which involved detailed item analysis on targeting, responsiveness, validity and reliability. Another 500 participants were recruited in Study 2 to replicate item analysis on validity and reliability on the refined item pool, and 250 of these participants re-completed the food literacy questionnaire to determine its test–retest reliability. RESULTS: The PCA saw the 171-item pool reduced to 100-items across 19 statistical components of food literacy. After the thresholds of 26 items were combined, responses to the food literacy questionnaire had ordered thresholds (targeting), acceptable item locations (< -0.01 to + 1.53) and appropriateness of the measurement model (n = 92% expected responses) (responsiveness), met outfit mean-squares MSQ (0.48—1.42) (validity) and had high person, item separation (> 0.99) and test–retest (ICC 2,1 0.55–0.88) scores (reliability). CONCLUSIONS: We developed a 100-item food literacy questionnaire, the IFLQ-19 to comprehensively address the Vidgen & Gallegos theoretical domains and components with good targeting, responsiveness, reliability and validity in a diverse sample of Australian adults. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12966-022-01351-8.