title: Validating an FFQ for intake of episodically consumed foods: application to the National Institutes of Health-AARP Diet and Health Study.
abstract: OBJECTIVE
  To develop a method to validate an FFQ for reported intake of episodically consumed foods when the reference instrument measures short-term intake, and to apply the method in a large prospective cohort.
  
  
  METHODS
  The FFQ was evaluated in a sub-study of cohort participants who, in addition to the questionnaire, were asked to complete two non-consecutive 24 h dietary recalls (24HR). FFQ-reported intakes of twenty-nine food groups were analysed using a two-part measurement error model that allows for non-consumption on a given day, using 24HR as a reference instrument under the assumption that 24HR is unbiased for true intake at the individual level.
  
  
  METHODS
  The National Institutes of Health-AARP Diet and Health Study, a cohort of 567 169 participants living in the USA and aged 50-71 years at baseline in 1995.
  
  
  METHODS
  A sub-study of the cohort consisting of 2055 participants.
  
  
  RESULTS
  Estimated correlations of true and FFQ-reported energy-adjusted intakes were 0·5 or greater for most of the twenty-nine food groups evaluated, and estimated attenuation factors (a measure of bias in estimated diet-disease associations) were 0·4 or greater for most food groups.
  
  
  CONCLUSIONS
  The proposed methodology extends the class of foods and nutrients for which an FFQ can be evaluated in studies with short-term reference instruments. Although violations of the assumption that the 24HR is unbiased could be inflating some of the observed correlations and attenuation factors, results suggest that the FFQ is suitable for testing many, but not all, diet-disease hypotheses in a cohort of this size.
authors.affiliation: Biometry Research Group, Division of Cancer Prevention, National Cancer Institute, Executive Plaza North - Suite 3131, 6130 Executive Blvd - MSC 7354, Bethesda, MD 20892-7354, USA. midthund@mail.nih.gov
authors.forename: Douglas
authors.initials: D
authors.lastname: Midthune
authors.forename: Arthur
authors.initials: A
authors.lastname: Schatzkin
authors.forename: Amy F
authors.initials: AF
authors.lastname: Subar
authors.forename: Frances E
authors.initials: FE
authors.lastname: Thompson
authors.forename: Laurence S
authors.initials: LS
authors.lastname: Freedman
authors.forename: Raymond J
authors.initials: RJ
authors.lastname: Carroll
authors.forename: Marina A
authors.initials: MA
authors.lastname: Shumakovich
authors.forename: Victor
authors.initials: V
authors.lastname: Kipnis
mesh_terms: D000368:Aged; D015331:Cohort Studies; D004032:Diet / Q000706:statistics & numerical data*; D004034:Diet Surveys / Q000295:instrumentation / Q000379:methods*; D002149:Energy Intake; D005260:Female; D006299:Health Services for the Aged; D006801:Humans; D008297:Male; D011939:Mental Recall; D008875:Middle Aged; D011446:Prospective Studies; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires / Q000592:standards*; D014481:United States