Dietary Reference Intakes: Applications in Dietary Assessment

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Dietary Reference Intakes: Applications in Dietary Assessment (2000)
Institute of Medicine (IOM)

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. "4 Using the Estimated Average Requirement for Nutrient Assessment of Groups." Dietary Reference Intakes: Applications in Dietary Assessment. Washington, DC: The National Academies Press, 2000.

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DRI DIETARY REFERENCE INTAKES: Applications in Dietary Assessment

Because the number of people in triangle A is approximately equal to the number in triangle B, these two groups cancel each other out, and the proportion of the population above the 45° line (inadequate intakes, shaded area of graph) 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) is about the same as the proportion of the population with intakes less than the EAR, even though some of the individuals in these two groups are not the same.

Box 4-2 The EAR cut-point method—when it works

The EAR cut-point method works best (produces an almost unbiased estimate of prevalence of nutrient inadequacy) when:

intakes and requirements are independent
the requirement distribution is symmetrical around the EAR
the variance in intakes is larger than the variance of requirements
true prevalence of inadequacy in the population is no smaller than 8 to 10 percent or no larger than 90 to 92 percent.

If the true prevalence in the group is about 50 percent—so that the mean intake is approximately equal to the EAR—then the EAR cut-point method results in almost unbiased estimates of prevalence of inadequacy even if conditions 1 and 3 are not met (see Appendix D).1

The EAR cut-point method—when it does not work

What happens when the assumptions required for the cut-point method are not met? In the following section, examples are provided of situations in which the assumptions do not hold. The cut-point method can either underestimate or overestimate the population prevalence of inadequacy under such circumstances.

Estimates of prevalence of inadequacy obtained using the EAR cut-point method are, by construction, slightly biased except when the mean intake and the EAR are similar. The relative bias in the prevalence estimate increases as the differencc between the mean intake in the group and the EAR of the nutrient increases. When true prevalence of inadequacy in the group is moderate (perhaps no less than 10 percent), the bias in the estimate arising from the EAR cut-point method is negligible as long as the conditions listed above are met. When true prevalence in the group is very small (perhaps between 1 and 3 percent), the relative bias can be very large—that is, the EAR cut-point method may result in an estimate of prevalence of 3 percent when the true prevalence is 1 or 2 percent.