title: Validity of nutrient estimates by food frequency questionnaires based either on exact frequencies or categories.
abstract: OBJECTIVE
  The study was designed to assess if category-based Food Frequency Questionnaires (FFQ) could be substituted for exact-frequency based questionnaires.
  
  
  METHODS
  Nutrient estimates on 203 subjects from Toronto, Canada, derived from recoding an exact frequency based 132 item food frequency questionnaire (E-FFQ) into categories were evaluated for validity against a 7-day food record (FR).
  
  
  RESULTS
  Among men, the median Pearson's correlation coefficient (for energy adjusted nutrients) between FR and E-FFQ was 0.53, ranging from 0.26 for thiamin to 0.72 for calcium. The median correlation dropped to a value of 0.40 (range: 0.18 for thiamin to 0. 56 for carbohydrate) when a category-based FFQ (C-FFQ) and FR were compared. Data on women showed a similar pattern; a median correlation of 0.50 from E-FFQ and 0.42 from C-FFQ.
  
  
  CONCLUSIONS
  While the results varied with individual nutrients, overall it is concluded that when validated against food records, the use of exact frequencies in FFQs yielded higher correlation coefficients for most nutrients, and slightly better agreement within quartiles of categories than recoded frequency categories.
authors.affiliation: Department of Public Health Sciences, University of Toronto, Ontario, Canada.
authors.forename: M
authors.initials: M
authors.lastname: Jain
authors.forename: J
authors.initials: J
authors.lastname: McLaughlin
mesh_terms: D000328:Adult; D000368:Aged; D004032:Diet; D016021:Epidemiologic Studies; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009749:Nutrition Surveys; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012737:Sex Factors; D011795:Surveys and Questionnaires / Q000592:standards*