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Abstract
Studies on the association between socioeconomic factors and food purchasing behavior have tended to rely on food expenditure data obtained through participant self-reports(1). However, self-reported expenditures have only rarely been compared to objective measures such as store and restaurant receipts collected over a given period of time(2–9). In addition, few receipt-based studies have addressed the disparities in the purchases of healthy or unhealthy foods across different socioeconomic status (SES) groups(3; 8).
The Seattle Obesity Study II (SOS II) collected store and restaurant receipts for 449 households over a period of 2 weeks. Participants were asked to report their monthly food expenditures for foods at home and away from home at the household level. The purpose of the present analyses was to: a) compare household food expenditures obtained from self-report vs. food shopping receipt data, using a number of validation techniques such as Pearson correlation, quintile kappa coefficient, and Bland-Altman method; b) examine socioeconomic trends in food expenditures using data from both methods: food shopping receipts vs. self-reports; c) to further examine SES trends in household food expenditures at home vs. away from home, as well as food groups using food shopping receipt data.
The food expenditure data from two methods showed moderate agreement with a Pearson correlation of .62, Kappa coefficient of .48, and Bland-Altman agreement of $3±$162 (mean ± Standard Deviation). Self-reported food expenditures adequately reflected objective data obtained by collecting food shopping receipts. Similar associations were observed between SES and food expenditure data, obtained from both the methods. Self-reported and receipt data showed that participants with higher SES spent significantly more on food. However, the percentage of income spent on food decreased as income increased. Further analyses of receipt data on eating out showed that higher income households spent a significantly higher percentage of food expenditure on eating-out as compared to lower income households (30.3% versus 18.7%). Higher income households spent a lower percentage of the food dollar in grocery stores (69.2% vs. 80.0%), and a greater percentage in full service restaurants (17.2% versus 6.8%) compared to lower income households. Produce purchases as percent of total were linked to educational attainment (23.8% vs. 14.5%). Purchases of sweetened beverages were linked to lower incomes (7.2% vs.9.6%). This study showed that self-reported expenditure is a valuable and cost-effective way to measure food spending.
