and survey-related effects, and interpreting the results appropriately. Assessment of groups for the adequacy of intake also involves choosing between two methods: (1) the probability approach or (2) the Estimated Average Requirement (EAR) cut-point method. Both are presented in detail in Chapter 4.

Individuals in a group vary both in the amounts of a nutrient they consume and in their requirements for the nutrient. If information were available on both the usual intakes and the requirements of all individuals in a group, determining the proportion of the group with intakes less than their requirements would be straightforward. One would simply observe how many individuals had inadequate intakes. Unfortunately, collecting such data is impractical. Therefore, rather than actually observing prevalence of inadequate intakes in the group, it can only be approximated by using other methods.

Regardless of the method chosen to actually estimate the prevalence of inadequacy, the EAR is the appropriate DRI to use when assessing the adequacy of group intakes. To demonstrate the pivotal importance of the EAR in assessing groups, the probability approach and the EAR cut-point method are described briefly below.

The probability approach is a statistical method that combines the distributions of requirements and intakes in the group to produce an estimate of the expected proportion of individuals at risk for inadequacy (NRC, 1986). For this method to perform well, little or no correlation should exist between intakes and requirements in the group. The concept is simple: at very low intakes the risk of inadequacy is high, whereas at very high intakes the risk of inadequacy is negligible. In fact, with information about the distribution of requirements in the group (median, variance, and shape), a value for risk of inadequacy can be attached to each intake level. Because there is a range of usual intakes in a group, the prevalence of inadequacy—the average group risk—is estimated as the weighted average of the risks at each possible intake level. Thus, the probability approach combines the two distributions: the requirement distribution which provides the risk of inadequacy at each intake level, and the usual intake distribution which provides the intake levels for the group and the frequency of each.