Monitoring Food Affordability: Reliability and Validity of an Online Nutritious Food Basket.

Purpose: This study aimed to assess the reliability and validity of an online approach to monitoring food affordability in Ontario using the updated Ontario Nutritious Food Basket (ONFB).Methods: The ONFB was priced online in 12 large multi-chain grocery stores to test intra-/inter-rater reliability using percent agreement and intra-class correlations (ICCs). Then, the ONFB was priced in-store and online in 28 stores to estimate food price differences using paired t-tests and Pearson's correlation for all (n =1708) and matched items (same product/brand and purchase unit) (n = 1134).Results: Intra-/inter-rater agreement was high (95.4%/81.6%; ICC = 0.972, F = 69.9, p < 0.001). On average, in-store prices were less than $0.02 lower than online prices. There were no significant differences between mean in-store and online prices for all items (t = 0.504 p = 0.614). The mean price was almost perfectly correlated between in-store and online (fully matched: R = 0.993 p < 0.001; all items: R = 0.967 p < 0.001). Online monthly ONFB estimates for a family of four were strongly correlated (R = 0.937 p < 0.001) with estimates calculated using in-store data.Conclusions: Online pricing is a reliable and valid approach to food costing in Ontario that contributes to modernizing the monitoring of food affordability in Canada and abroad.