Dietary Reference Intakes Applications in Dietary Assessment (2000) / Chapter Skim
Currently Skimming:
4 Using the Estimated Average Requirement for Nutrient Assessment of Groups
4 Using the Estimated Average Requirement for Nutrient Assessment of Groups
Pages 73-105
The Chapter Skim interface presents what we've algorithmically identified as the most significant single chunk of text within every page in the chapter.
Select key terms on the right to highlight them within pages of the chapter.
From page 73... ...
To accurately determine the proportion of a group that has a usual intake of a nutrient less than the requirement, information on both usual intakes and nutrient requirements for each incliviclual in the group is needed. With this information, assessing how many inclivicluals have intakes that do not meet their incliviclual requirements is straightforward.
|
From page 74... ...
Presented in this chapter is an abbreviated description of a statistical approach to estimating the prevalence of inadequate intakes the probability approach and a shortcut to the probability approach referred to as the EAR cut-point method. Both of these require the use of the EAR.
|
From page 75... ...
1,200 unitsJ, some people in the population still have intakes below their requirements. Simply comparing the average intake to the average requirement does not answer the question about how many in a group have inadequate intakes.
|
From page 76... ...
THE PROBABILITYAPPROACH The ciata typically available for nutrient assessment include estimated univariate distributions of usual intakes for a group of indivicluals and information from estimated univariate distributions of nutrient requirements of other groups that are similar to the group
|
From page 77... ...
Intake equal to the mean requirement of 100 units has a 50 percent risk of inadequacy (the definition of the Estimated Average Requirement [EAR]
|
From page 78... ...
.. 30 60 90 120 150 180 Intake levels ._ o >I c' IL FIGURE 4-4 Risk curve combined with a usual intake distribution where the mean intake is less than the Estimated Average Requirement (EAR)
|
From page 79... ...
10080 C' 60— 40o .m 20 105-_ , Intake of / 1 OO=EAR / \ '\ ' \ ' \ \ ,~, \ < O - , 50 Mean Intake=150 75 1 00 125 150 175 200 Intake levels In ._ a c' 250 FIGURE 4-5 Risk curve combined with a usual intake distribution where the mean intake is much higher than the Estimated Average Requirement (EAR)
|
From page 80... ...
\ ~ it L ~ \ ~ ~(115~~25) \ 0 30 1 1 T r r T 1 60 70 80 90 100 110 120 Intake levels (a ._ so IL T 1 T 1 40 1 50 1 60 1 80 FIGURE 4-6 Risk curve combined with a usual intake distribution where mean intake (115 units)
|
From page 81... ...
for the nutrient and the distribution of usual intakes in the population. Table 4-1 summarizes whether nutrients for which Dietary Reference Intakes (DRIB)
|
From page 82... ...
. In the example used when discussing the probability approach, population prevalence according to the EAR cut-point method would be the proportion of inclivicluals with usual intakes below 100 units, the EAR.
|
From page 83... ...
The figure includes joint intake and requirement data from 3,000 people, with a mean intake of 1,600 units and a mean requirement of 1,200 units. As before, intakes and requirements are inclepenclent (i.e., inclivicluals with higher intakes are not more likely to have higher requirements)
|
From page 84... ...
were above the 45° line. Most of the people who do not meet their requirements have intakes below 1,200 units the median requirement, clenoteci in Figure 4-8 by the vertical line labeled intake = EAR.
|
From page 85... ...
The mean intake is 1,600 units and the median requirement (Estimated Average Requirement [EAR]
|
From page 86... ...
is approximately equal to the proportion of the population to the left of the intake = EAR line. In other words, the proportion of the population with intakes below their requirements (from the joint distribution approach)
|
From page 87... ...
Using the Estimated Average Requirement (EAR) cut-point method would overestimate the number of people with inadequate intakes.
|
From page 88... ...
An exception to this rule is the extreme case in which the correlation between intakes and requirements of the nutrient is equal to 1. In this unlikely event, the prevalence estimates obtained from the EAR cut-point method will be severely biased, even if mean intake and the EAR are identical.
|
From page 89... ...
. example of both a perfect correlation between individual intakes and requirements and mean intake equal to the average requirement.
|
From page 90... ...
The Estimated Average Requirement (EAR) cut-point method would result in an underestimate of the true prevalence of inadequacy.
|
From page 91... ...
At least in North America, the situation where variation in indiviclual requirements is greater than variation in incliviclual usual intakes is most likely to arise for institutionalized subpopulationsfor example, prison inmates or residents of a long-term care facility who are all fed similar diets. Figure 4-11 illustrates this scenario:
|
From page 92... ...
has been set at 1,400 units and the mean of the usual intake distribution has been set at 1,600 units. Note that although the mean intake exceeds the meclian requirement, there is much more spread in requirements than there is in intake.
|
From page 93... ...
The over- or underestimation of true prevalence is more pronounced when the true prevalence in the group is either very low or very high. ADJUSTING INTAKE DISTRIBUTIONS Regardless of the method chosen to assess prevalence of inaclequate nutrient intakes in a group of inclivicluals, information is required about the distribution of intakes of the nutrient in the group.
|
From page 94... ...
Reasons for Adjusting Intake Distributions Several characteristics of clietary intake ciata make estimating the distribution of usual intakes for a group a challenging problem. This section focuses on the neeci for adjustment of distributions, illustrates the use of two of the most widely used approaches, and discusses the consequences of poorly estimating usual intake clistributions.
|
From page 95... ...
Inclivicluals with higher average intakes also tend to have more variable intakes than do inclivicluals with lower average intakes (Nusser et al., 1996~. Skewed Intake Distributions For most nutrients, the distribution of observed mean intakes (and presumably, the usual intake distribution as well)
|
From page 96... ...
The NRC, in its 1986 report, set forth the concept of a usual intake distribution, and proposed a statistical approach to adjust observed mean intake distributions to partially remove the ciay-to-ciay variability in intakes. The resulting estimated usual intake distribution has a spread that approximately reflects the between-individual variability in intakes (NRC, 1986~.
|
From page 97... ...
The National Research Council Method to Adjust Intake Distributions In recognizing that ciaily intakes for an incliviclual vary from clay to clay, and that ciaily intake ciata are not normally clistributeci, the NRC (1986) proposed that ciay-to-ciay variability in intakes be partially removed by fitting a measurement error model to ciaily intake ciata which haci been power transformed.
|
From page 98... ...
How large a sample size, and what proportion of replicate observations are neecleci for the ISU method of estimating usual nutrient intake distributions? An exact answer to this question is difficult to provide.
|
From page 99... ...
successfully applied the ISU method to adjust intake distributions and distributions of blood biochemical measurements using ciata collected in the Third National Health and Nutrition Examination Survey (NHANES III) , even though sample sizes for some life stage and gentler groups were moderately small (fewer than 70 to 80 inclivicluals)
|
From page 100... ...
5 6 7 FIGURE 4-12 Estimates of a usual intake distribution of vitamin B6 obtained from one day of intake data and adjusted using replicate intake data via the Iowa State University method. The Taxis shows the likelihood of each level of intake in the population.
|
From page 101... ...
\ Adjusted intake \ _ _ _ Day 1 intake \ / / / / / / ,~ J ///l -\\~ \ 0 500 1000 1 500 2000 2500 Intake levels of phosphorus (mg) 101 3000 3500 FIGURE 4-13 Estimates of a usual intake distribution of phosphorus obtained from one day of intake data and adjusted using replicate intake data via the Iowa State University method.
|
From page 102... ...
As inclicatecT previously in this chapter, the proportion of inclivicluals in a group with nutrient intakes below their requirements can be estimated by using the Estimated Average Requirement (EAR) cut-point method (calculating the proportion of inclivicluals in the group with intakes below the EAR)
|
From page 103... ...
An even stronger caution is neecleci when comparing group mean intakes with the EAR. If mean intake equals the average requirement (EAR)
|
From page 104... ...
that is relevant to this type of assessment is the Estimated Average Requirement (EAR)
|
From page 105... ...
USE OF EARs FOR NUTRIENT ASSESSMENT 105 women requires use of the probability approach because of the highly skewoci nature of the requirement distributions Because of the very high correlation between intakes and requirements, energy is the one nutrient for which neither the probability approach nor the cut-point method can be used to assess acloquacy. The prevalence of nutrient inacloquacy for a group will usually be overestimated by either method if clietary intake ciata are not acljusteci for ciay-tociay within-person variation.
|
Key Terms
This material may be derived from roughly machine-read images, and so is provided only to facilitate research.
More
information on Chapter Skim is available.