To compute the risk to attach to each intake level, one needs to know the EAR (the median) of the requirement distribution as well as its variance and its shape. Without an EAR, the probability approach cannot be used to estimate the prevalence of inadequacy.
With some additional assumptions, a simpler version of the probability approach can be applied with essentially the same success. The EAR cut-point method can be used if no correlation exists between intakes and requirements (as in the probability approach above), if the distribution of requirements can be assumed to be symmetrical around the EAR, and if the variance of intakes is greater than the variance of requirements. Table S-1 indicates whether these conditions have been met for nutrients for which DRIs have been determined at the time of publication.
The EAR cut-point method is simpler because rather than estimating the risk of inadequacy for each individual's intake level, one simply counts how many individuals in the group of interest have usual intakes that are below the EAR. That proportion is the estimate of the proportion of individuals in the group with inadequate intakes. (For a theoretical justification of this simplified cut-point method, see Chapter 4 or Appendix C and Appendix D.)
Regardless of the method chosen to assess prevalence of inadequate nutrient intakes in a group of individuals, information is required about the distribution of usual intakes of the nutrient in the group. The distribution of those usual intakes in the group is referred to as the usual intake distribution or the adjusted intake distribution. Adjustments to the distribution of observed intakes are needed to partially remove the day-to-day variability in intakes (within-person variation). The resulting estimated usual intake distribution of a dietary component should then better reflect the individual-to-individual variation of intakes of that component within the group.
Usual intake distributions can be estimated by statistically adjusting the distribution of intake of each individual in the group. This general approach was proposed by NRC (1986) and was further developed by Nusser et al. (1996). To adjust intake distributions, it is necessary to have at least two independent days of dietary intake data for a representative subsample of individuals in the group (or at least three days when data are collected over consecutive days).