ment, and then count the number of people in the group who do not meet their requirement.
What proportion of individuals in a group has a usual intake of a nutrient that is less than the requirement for that nutrient? This is one of the most basic questions that can be asked about nutrient intakes, and is critically important from a public health perspective. Clearly, the implications would differ if 30 versus 3 percent of individuals in the population had usual intakes that were inadequate to meet estimated needs. 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. |
Consider a purely hypothetical example of a group comprised of 24 individuals, whose intakes of and requirements for a nutrient are known. The data for these individuals are plotted in Figure 4-1.
In this figure, the 45° line represents the points at which intake equals requirement. The individual labeled “A” in the plot has an intake of the nutrient of 7 units and a requirement for the nutrient of 11 units. Points that fall below (or to the right of) the 45° line are for individuals whose usual intakes are greater than their requirements, whereas points above (or to the left of) the line (the shaded area) are for individuals whose usual intakes are less than their requirements. Six individuals have inadequate intakes, corresponding to the six points above the line. Thus, for this group, the prevalence of inadequate intakes is (6/24) × 100, or 25 percent.
A second example illustrates the same approach with a larger sample. Figure 4-2 shows hypothetical intakes and requirements for a nutrient in a group of 3,000 people. Both the requirement distribution and the intake distribution are assumed to be normal, and not correlated. That is, people who have high requirements do not have a tendency to consume more and thus have greater intakes. The average requirement for the nutrient is 1,200 units and the standard deviation of the requirement is 180 units. The mean of the usual intakes of 3,000 people is 1,600 units and the standard deviation for intake for this group is 450 units. Note that the average usual intake (1,600) is greater than the average requirement (1,200) and that there is more variability (spread) in intakes than there is in requirements. This is the usual situation for most nutrient intakes and requirement distributions.