title: Sources of variation in nutrient intakes among men in Shanghai, China.
abstract: OBJECTIVE
  Random errors, from any source, will attenuate epidemiological risk estimates. Before we launched the Shanghai Men's Health Study (SMHS), a large population-based cohort study investigating the diet-cancer association among Chinese men, a dietary calibration study was conducted among 96 men aged 40-75 years (mean age 56.5 years), with biweekly 24-hour dietary recalls (24HDRs) implemented over a 1-year period. Data from this study were analysed to evaluate the nature and magnitude of variances for intake of 26 nutrients among SMHS participants, to compare variance ratios of 26 nutrients among Chinese men and women and individuals in other studies, and to estimate the number of 24HDRs required for future dietary calibration studies in similar populations.
  
  
  METHODS
  Ninety-six healthy, free-living men in Shanghai were administered biweekly 24HDR interviews 24 times over a 1-year period. To assess between-individual and within-individual contributions to variance, a mixed effects model was fitted and ratios of within-individual to between-individual (sigma(w)(2)/sigma(b)(2)) dietary intake variances were computed.
  
  
  METHODS
  Shanghai, China.
  
  
  RESULTS
  In agreement with reports from studies conducted in the USA and many other countries, we found that within-individual variances were usually larger than between-individual variances in dietary intake for all nutrients. The sum of all other variation (e.g. weekday and weekend, seasonal, interviewer) accounted for less than 5% of total variation. Ratios of within- to between-individual variances (for log-transformed data) ranged from 1.25 for carbohydrate intake to near 8 for delta-tocopherol intake.
  
  
  CONCLUSIONS
  The results of this study suggest that among middle-aged and elderly Chinese men in Shanghai, within- and between-individual variation account for more than 95% of the total variation for 26 nutrients. Further dietary validation studies in the same population could be adequately carried out with only 12 days of dietary recalls, if 100 participants were enrolled.
authors.affiliation: Department of Medicine, Center for Health Services Research and Vanderbilt-Ingram Cancer Center, 6009 MCE, Vanderbilt University, 1215 21st Avenue, Nashville, TN 37232-8300, USA.
authors.forename: Hui
authors.initials: H
authors.lastname: Cai
authors.forename: Gong
authors.initials: G
authors.lastname: Yang
authors.forename: Yong-Bing
authors.initials: YB
authors.lastname: Xiang
authors.forename: James R
authors.initials: JR
authors.lastname: Hebert
authors.forename: Da-Ke
authors.initials: DK
authors.lastname: Liu
authors.forename: Wei
authors.initials: W
authors.lastname: Zheng
authors.forename: Xiao-Ou
authors.initials: XO
authors.lastname: Shu
mesh_terms: D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D002681:China; D015331:Cohort Studies; D004032:Diet / Q000592:standards / Q000706:statistics & numerical data; D004034:Diet Surveys; D005247:Feeding Behavior; D006801:Humans; D008297:Male; D011939:Mental Recall; D008875:Middle Aged; D015203:Reproducibility of Results; D012621:Seasons; D012680:Sensitivity and Specificity; D011795:Surveys and Questionnaires