title: Calibration of the dietary questionnaire for the Canadian Study of Diet, Lifestyle and Health cohort.
abstract: OBJECTIVE
  For proper interpretation of results from epidemiological studies that use food-frequency questionnaires (FFQs), it is necessary to know the relationship between reported intakes from the FFQ and true usual intake. In this paper, we report a calibration study conducted to investigate the performance of the FFQ used in a cohort study, the Canadian Study of Diet, Lifestyle and Health.
  
  
  METHODS
  Over a 1-year period, 151 men and 159 women completed a full set of questionnaires including a self-administered baseline FFQ, three 24-hour diet recalls administered by telephone, and a second FFQ self-administered subsequently. The association between the nutrient estimates derived from the FFQs and the diet recalls was evaluated by calculating deattenuated Pearson's correlation coefficients.
  
  
  RESULTS
  FFQs estimated mean daily nutrient intakes higher than the diet recalls. When the log-transformed and energy-adjusted nutrient intakes from the average of three 24-hour recalls were compared against the baseline FFQ, the following deattenuated correlations were obtained in men and women, respectively: total energy 0.44 and 0.32, total fat 0.64 and 0.68, saturated fat 0.68 and 0.70, dietary fibre 0.65 and 0.44, vitamin E 0.32 and 0.37, vitamin C 0.40 and 0.37, beta-carotene 0.34 and 0.29, alcohol 0.74 and 0.67, caffeine 0.81 and 0.76, with a median correlation of 0.49 and 0.53. Correlations between the second FFQ and diet recalls were similar. The correlations between the two FFQs as a test of reliability had a median value 0.64 for men and 0.63 for women for selected nutrients.
  
  
  CONCLUSIONS
  The study suggests that the FFQ method gives acceptable levels of nutrients or food component estimates, as assessed by this calibration study against diet recalls, when limited to energy-adjusted and deattenuated values.
authors.affiliation: Department of Public Health Sciences, University of Toronto, Ontario, Canada. meera.jain@utoronto.ca
authors.forename: Meera G
authors.initials: MG
authors.lastname: Jain
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Rohan
authors.forename: Colin L
authors.initials: CL
authors.lastname: Soskolne
authors.forename: Nancy
authors.initials: N
authors.lastname: Kreiger
mesh_terms: D002138:Calibration; D002170:Canada; D015331:Cohort Studies; D004032:Diet; D004034:Diet Surveys; D005260:Female; D006801:Humans; D008297:Male; D011939:Mental Recall; D008875:Middle Aged; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires / Q000592:standards*