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Nutrient Adequacy Assessment Using Food Consumption Surveys (1986) / Chapter Skim
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4. The Use of Short-Term Dietary Intake Data to Estimate Usual Dietary Intake
Pages 17-24

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From page 17...
... RELATIONSHIP OF DAILY DIETARY INTAKE DATA TO USUAL INTAKE: Many authors have compared the reliability of data from 1-day dietary intake records and records for longer periods (Garn et al., 1978; Marr, 1971; PeRkarinen, 1970; Young et al., 1952a) , and errors in usual intake estimation due to intraindividual variation have attracted considerable interest.
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From page 18...
... As a result of the phenomenon of intraindividual variation, when one uses a fixed cutoff point for an observed intake distribution, the number of days on which intake was recorded affects the apparent prevalence of inadequate intake (Hegsted, 1972)
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From page 19...
... This is illustrated in Table 4-1, which presents the ratio of intra- to interindividual variance for various studies by nutrient and sex. Several authors noted that for nutrients with markedly skewed distributions, the ratios for logarithmically transformed intake distributions were lowered (Beaton et al., 1983; Hunt _ al., 1983; Sempos et al., 1985)
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From page 20...
... bThe original papers contain additional data. Only those nutrient variables examined in two or more papers are included here.
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From page 21...
... PROCEDURE FOR ADJUSTING INTAKE DATA When the intraindividual variation of dietary intake and the nether of days of observation are known, it is possible to determine reliability of dietary intake data for each particular person. The usual intake for each person lies within the bounds described by the following equation 95% of the time if the day-to-day variations are normally distributed: + 2 x SD (intra)
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From page 22...
... In this equation, the interindividual variation represents the distribution of usual intake referred to previously. Statistical theory allows us to derive an estimate of the distribution of usual intakes, given the observed mean, the total variance, and an estimate of the intraindividual variance.
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From page 23...
... \ '1 Am\ 1 -DAY I NTAKE g - __ 6.3 12.6 ~ 8.9 25.2 31.5 I RON I NTAK E, mg/day FIGURE 4-3. Comparison of 1-day and adjusted distributions for iron intake by female adults.
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From page 24...
... If the survey data include an adequate number of independent replicate observations of intake measurements, methods can be used to adjust the observed intake distribution to generate a good estimate of the distribution of usual intakes. In a large survey, such as the NFCS, this approach is feast ble and may even permit collection of fewer data than are now collected, given an appropriate sampling design.
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Key Terms

  • intake data
  • intraindividual variation
  • usual intake
  • usual intakes
  • usual dietary

  • interindividual variation
  • energy intake
  • intake distribution
  • intake distributions
  • intraindividual component

  • total variance
  • lipid levels
  • observed intake
  • estimate usual
  • reliable estimates

  • fixed cutoff
  • apparent prevalence
  • confidence limits
  • consecutive days
  • intraindividual variance

  • intake contributes
  • skewed distributions
  • following equation
  • tar menf
  • transformed intake

  • inadequate intake
  • actual magnitude
  • bounds described
  • consumption survey
  • observation increases


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