title: Relative validity and reproducibility of a quantitative FFQ for assessing nutrient intakes of vegetarians in Taiwan.
abstract: OBJECTIVE
  To assess the relative validity and reproducibility of the quantitative FFQ used in the Tzu Chi Health Study (TCHS).
  
  
  METHODS
  The reproducibility was evaluated by comparing the baseline FFQ with the 2-year follow-up FFQ. The validity was evaluated by comparing the baseline FFQ with 3 d dietary records and biomarkers (serum folate and vitamin B12). Median comparison, cross-classification and Spearman correlation with and without energy adjustment and deattenuation for day-to-day variation were assessed.
  
  
  METHODS
  TCHS is a prospective cohort containing a high proportion of true vegetarians and part-time vegetarians (regularly consuming a vegetarian diet without completely avoiding meat).
  
  
  METHODS
  Subsets of 103, seventy-eight and 1528 TCHS participants were included in the reproducibility, dietary record-validity and biomarker-validity studies, respectively.
  
  
  RESULTS
  Correlations assessing the reproducibility for repeat administrations of the FFQ were in the range of 0·46-0·65 for macronutrients and 0·35-0·67 for micronutrients; the average same quartile agreement was 40%. The correlation between FFQ and biomarkers was 0·41 for both vitamin B12 and folate. Moderate to good correlations between the baseline FFQ and dietary records were found for energy, protein, carbohydrate, saturated and monounsaturated fat, fibre, vitamin C, vitamin A, K, Ca, Mg, P, Fe and Zn (average crude correlation: 0·47 (range: 0·37-0·66); average energy-adjusted correlation: 0·43 (range: 0·38-0·55); average energy-adjusted deattenuated correlation: 0·50 (range: 0·44-0·66)) with same quartile agreement rate of 39% (range: 35-45%), while misclassification to the extreme quartile was rare (average: 4% (range: 0-6%)).
  
  
  CONCLUSIONS
  The FFQ is a reliable and valid tool to rank relative intake of major nutrients for TCHS participants.
authors.affiliation: 1Medical Mission,Tzu Chi Foundation,Hualien,Taiwan.
authors.forename: Tina H T
authors.initials: TH
authors.lastname: Chiu
authors.affiliation: 2Department of Family Medicine,Buddhist Dalin Tzu Chi General Hospital,No. 2 Min-Sheng Road,Dalin Town,Chiayi County,Taiwan62247.
authors.forename: Hui-Ya
authors.initials: HY
authors.lastname: Huang
authors.affiliation: 3Department of Hospitality Management,Chung-Hwa University of Medical Technology,Tainan,Taiwan.
authors.forename: Kuan-Ju
authors.initials: KJ
authors.lastname: Chen
authors.affiliation: 2Department of Family Medicine,Buddhist Dalin Tzu Chi General Hospital,No. 2 Min-Sheng Road,Dalin Town,Chiayi County,Taiwan62247.
authors.forename: Yu-R U
authors.initials: YR
authors.lastname: Wu
authors.affiliation: 4Department of Computer Science,University of British Columbia,Vancouver,BC,Canada.
authors.forename: Jason P C
authors.initials: JP
authors.lastname: Chiu
authors.affiliation: 5Department of Public Health,Tzu Chi University,Hualien,Taiwan.
authors.forename: Yi-Hwei
authors.initials: YH
authors.lastname: Li
authors.affiliation: 6Department of Health Studies,University of Chicago,Chicago,IL,USA.
authors.forename: Brian C-H
authors.initials: BC
authors.lastname: Chiu
authors.affiliation: 1Medical Mission,Tzu Chi Foundation,Hualien,Taiwan.
authors.forename: Chin-Lon
authors.initials: CL
authors.lastname: Lin
authors.affiliation: 2Department of Family Medicine,Buddhist Dalin Tzu Chi General Hospital,No. 2 Min-Sheng Road,Dalin Town,Chiayi County,Taiwan62247.
authors.forename: Ming-Nan
authors.initials: MN
authors.lastname: Lin
mesh_terms: D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000097:blood; D015930:Diet Records; D004034:Diet Surveys / Q000592:standards*; D014676:Diet, Vegetarian; D005247:Feeding Behavior; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015596:Nutrition Assessment; D009753:Nutritive Value; D011446:Prospective Studies; D015203:Reproducibility of Results; D011795:Surveys and Questionnaires / Q000592:standards*; D013624:Taiwan
chemical_list: D015415:Biomarkers