title: Measuring diet cost at the individual level: a comparison of three methods.
abstract: OBJECTIVE
  Household-level food spending data are not suitable for population-based studies of the economics of nutrition. This study compared three methods of deriving diet cost at the individual level.
  
  
  METHODS
  Adult men and women (n=164) completed 4-day diet diaries and a food frequency questionnaire (FFQ). Food expenditures over 4 weeks and supermarket prices for 384 foods were obtained. Diet costs (US$/day) were estimated using: (1) diet diaries and expenditures; (2) diet diaries and supermarket prices; and (3) FFQs and supermarket prices. Agreement between the three methods was assessed on the basis of Pearson correlations and limits of agreement. Income-related differences in diet costs were estimated using general linear models.
  
  
  RESULTS
  Diet diaries yielded mean (s.d.) diet costs of $10.04 (4.27) based on Method 1 and $8.28 (2.32) based on Method 2. FFQs yielded mean diet costs of $7.66 (2.72) based on Method 3. Correlations between energy intakes and costs were highest for Method 3 (r(2)=0.66), lower for Method 2 (r(2)=0.24) and lowest for Method 1 (r(2)=0.06). Cost estimates were significantly associated with household incomes.
  
  
  CONCLUSIONS
  The weak association between food expenditures and food intake using Method 1 makes it least suitable for diet and health research. However, merging supermarket food prices with standard dietary assessment tools can provide estimates of individual diet cost that are more closely associated with food consumed. The derivation of individual diet cost can provide insights into some of the economic determinants of food choice, diet quality and health.
authors.affiliation: 1] UKCRC, Centre for Diet and Activity Research, University of Cambridge, Institute for Public Health, Cambridge, UK [2] Department of Public Health and Primary Care, University of Cambridge, CB1 8RN, UK [3] School of Public Health, University of Washington, Seattle, WA, USA.
authors.forename: P
authors.initials: P
authors.lastname: Monsivais
authors.forename: M M
authors.initials: MM
authors.lastname: Perrigue
authors.forename: S L
authors.initials: SL
authors.lastname: Adams
authors.forename: A
authors.initials: A
authors.lastname: Drewnowski
mesh_terms: D000328:Adult; D000368:Aged; D003132:Commerce; D003365:Costs and Cost Analysis; D004032:Diet / Q000191:economics*; D015930:Diet Records; D002149:Energy Intake; D005191:Family Characteristics; D005247:Feeding Behavior; D005260:Female; D005523:Food Supply / Q000191:economics*; D006801:Humans; D007182:Income; D008297:Male; D008875:Middle Aged; D015596:Nutrition Assessment; D009752:Nutritional Status; D011795:Surveys and Questionnaires
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