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Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate
lar) is usually assumed for nutrient requirements. At this level of intake, half of the members of a specified group would not have their nutritional needs met. The general method used to set the EAR is the same for all the nutrients. For many of the nutrients, including those in this report, there are few direct data on the requirements of children. Thus, for such nutrients, EARs and RDAs for children are based on extrapolations from adult values. The methods used for extrapolation are described in Chapter 2.
Method for Setting the RDA When Nutrient Requirements Are Normally Distributed
If the requirement for the nutrient is normally distributed, and the standard deviation (SD) of the EAR is available, the RDA is defined as equal to the EAR plus 2 SDs of the EAR:
If data about variability in requirements are insufficient to calculate an SD, a coefficient of variation (CVEAR) of 10 percent will be ordinarily assumed and used to estimate the SD:
The resulting equation for the RDA is
The assumption of a 10 percent CV is based on extensive data on the variation in basal metabolic rate (FAO/WHO/UNA, 1985; Garby and Lammert, 1984), which contributes about two-thirds of the daily energy needs of many individuals residing in Canada and the United States (Elia, 1992), and on the similar CV of 12.5 percent estimated for the protein requirements in adults (FAO/WHO/ UNA, 1985).