title: Validation of a food-frequency questionnaire using multiple-day records and biochemical markers: application of the triads method.
abstract: BACKGROUND
  A food-frequency questionnaire (FFQ) used to assess usual food intake in Southern France has been validated by the classical means of multiple-day food records. To minimise over-estimation of the correlation between the dietary assessments by the FFQ and the reference method, which occurs if the random errors of questionnaire and reference measurement are positively correlated, a triangular comparison, the method of triads, was used.
  
  
  METHODS
  We applied the triads model by comparing the FFQ with two multiple-day food records and three biomarkers. Only 87 subjects were included and completed the protocol. One biomarker (beta-carotene) was used for the 87 subjects and two biomarkers (urinary nitrogen and potassium) were measured in only 40 subjects.
  
  
  RESULTS
  For beta-carotene intake assessment, the triad model, including the weighed multiple records (PETRA), was the best with estimates of validity coefficient of 0.39 [confidence interval (CI) 0.18-0.60] for the FFQ, 0.52 (CI 0.24-0.86), for PETRA and 0.85 (CI 0.43-1) for plasma levels of the nutrient. For protein and potassium intake assessment, the triad model including the estimated multiple records was the best only for the estimates of FFQ validity coefficient (0.61; CI 0.28-0.96 and 0.31; CI 0.09-0.66 respectively).
  
  
  CONCLUSIONS
  Accuracy of the dietary assessment methods permitted a satisfactory estimation of the validity coefficient for beta-carotene intake by the FFQ, despite a small sample. However, the validity coefficients for protein and potassium showed wide CI values, indicating that a sample size < 50 subjects appears unsatisfactory for validation.
authors.affiliation: Département de Biostatistique, Institut Universitaire de Recherche Clinique, Montpellier, France.
authors.forename: J P
authors.initials: JP
authors.lastname: Daurès
authors.forename: M
authors.initials: M
authors.lastname: Gerber
authors.forename: J
authors.initials: J
authors.lastname: Scali
authors.forename: C
authors.initials: C
authors.lastname: Astre
authors.forename: C
authors.initials: C
authors.lastname: Bonifacj
authors.forename: R
authors.initials: R
authors.lastname: Kaaks
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000032:analysis*; D002851:Chromatography, High Pressure Liquid; D004032:Diet; D004044:Dietary Proteins; D005260:Female; D005602:France; D006801:Humans; D008055:Lipids / Q000097:blood; D008297:Male; D015233:Models, Statistical; D009584:Nitrogen / Q000652:urine; D015596:Nutrition Assessment; D011188:Potassium / Q000652:urine; D011795:Surveys and Questionnaires; D019207:beta Carotene / Q000097:blood
chemical_list: D015415:Biomarkers; D004044:Dietary Proteins; D008055:Lipids; D019207:beta Carotene; D009584:Nitrogen; D011188:Potassium