individuals in the group whose usual intakes are less than the EAR (Beaton, 1994) (Figure 13-1). The estimate is most accurate if the variability of intakes is at least twice as large as the variability of requirements. Before intake is compared with the EAR, methods should be used to remove the day-to-day variation in intake (Nusser et al., 1996) so that the intake data better reflect usual intakes. The adjustment narrows the intake distribution and thus gives a better estimate of the percentage of the group with intakes below the EAR (Figure 13-2).

Examples of estimating the prevalence of inadequate intake appear in Figures 13-3 and 13-4, which use adjusted data from the Third National Health and Nutrition Examination Survey. A large percentage of adults reportedly have a total folate intake less than the EAR (Figure 13-3), and this percentage is greater for women than for men. However, because the reported folate intake is considered to be substantially underestimated (partly because of methodological problems, partly because adjustment has not been made for the better bioavailability of folate in fortified cereals, and partly because these data were obtained before the fortification of cereal grains with folate was required), it is not known to what extent this

FIGURE 13-1 Estimation of the population prevalence of inadequate intakes. For this method to apply, the variance of intakes must be greater than the variance of requirements, and the requirement distribution must be symmetrical. EAR = Estimated Average Requirement.