Validating self-reported food expenditures against food store and eating-out receipts.
OBJECTIVE
To compare objective food store and eating-out receipts with self-reported household food expenditures.


METHODS
The Seattle Obesity Study 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 to 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 with receipts using paired t-tests, Bland-Altman plots and κ-statistics. Bias by sociodemographics 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 to 143.4 for total food expenditures, mean difference 5.7 for food stores and mean difference 1.7 for eating out. The κ-statistics showed good agreement for each (κ 0.51, 0.41 and 0.49 respectively. Households with higher education and income had significantly more number of receipts and higher food expenditures.


CONCLUSIONS
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.
Center for Public Health Nutrition, University of Washington, Seattle WA, USA.
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Tang
Center for Public Health Nutrition, University of Washington, Seattle WA, USA.
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Aggarwal
Center for Public Health Nutrition, University of Washington, Seattle WA, USA.
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Liu
Center for Public Health Nutrition, University of Washington, Seattle WA, USA.
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M
Acheson
Center for Public Health Nutrition, University of Washington, Seattle WA, USA.
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Rehm
Urban Form Lab, University of Washington, Seattle WA, USA.
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Moudon
Center for Public Health Nutrition, University of Washington, Seattle WA, USA.
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Drewnowski
D000328:Adult; D003258:Consumer Behavior; D003365:Costs and Cost Analysis; D005191:Family Characteristics; D005260:Female; D005500:Follow-Up Studies; D005502:Food / Q000191:economics*; D006801:Humans; D008297:Male; D008875:Middle Aged; D009749:Nutrition Surveys; D011446:Prospective Studies; D015203:Reproducibility of Results; D057566:Self Report; D012959:Socioeconomic Factors; D014861:Washington; D055815:Young Adult