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

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). 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). Intra-/inter-rater agreement was high (95.4%/81.6%; ICC = 0.972, F = 69.9,  < 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  = 0.614). The mean price was almost perfectly correlated between in-store and online (fully matched: R = 0.993  < 0.001; all items: R = 0.967  < 0.001). Online monthly ONFB estimates for a family of four were strongly correlated (R = 0.937  < 0.001) with estimates calculated using in-store data. 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.