Validating self-reported food expenditures against food store and eating-out receipts

OBJECTIVES: To compare objective food store and eating-out receipts with self-reported household food expenditures. DESIGN AND SETTING: The Seattle Obesity Study (SOS II) was based on a representative sample of King County adults, Washington, USA. Self-reported household food expenditures were modeled on the Flexible Consumer Behavior Survey (FCBS) Module from 2007–2009 National Health and Nutrition Examination Survey (NHANES). Objective food expenditure data were collected using receipts. Self-reported food expenditures for 447 participants were compared to receipts using paired t-tests, Bland-Altman plots, and kappa statistics. Bias by socio-demographics was also examined. RESULTS: Self-reported expenditures closely matched with objective receipt data. Paired t-tests showed no significant differences between receipts and self-reported data on total food expenditures, expenditures at food stores, or eating out. However, the highest income strata showed weaker agreement. Bland Altman plots confirmed no significant bias across both methods - mean difference: 6.4; agreement limits: −123.5, 143.4 for total food expenditures, mean difference 5.7 for food stores, and mean difference 1.7 for eating-out. Kappa statistics showed good agreement for each (kappa 0.51, 0.41 and 0.49 respectively. Households with higher education and income had significantly more number of receipts and higher food expenditures. CONCLUSION: Self-reported food expenditures using NHANES questions, both for food stores and eating-out, serve as a decent proxy for objective household food expenditures from receipts. This method should be used with caution among high income populations, or with high food expenditures. This is the first validation of the FCBS food expenditures question using food store and eating-out receipts.