Each type of DRI refers to average daily nutrient intake over time. Some deviation around this average value over a number of days is expected.
The Estimated Average Requirement (EAR) is the daily intake value that is estimated to meet the requirement, as defined by the specified indicator of adequacy, in 50 percent of the individuals in a life stage or gender group (see Figure 1-1). At this level of intake, the other 50 percent of individuals in a specified group would not have their nutritional needs met. The EAR is used in setting the RDA (see below).
The Recommended Dietary Allowance (RDA) is the average daily dietary intake level that is sufficient to meet the nutrient requirements of nearly all (97 to 98 percent) healthy individuals in a specific life stage and gender group (see Figure 1-1). The RDA is intended primarily for use as a goal for daily intake by individuals.
The EAR forms the basis for setting the RDA. If the variation in requirements is well defined and the requirement is normally distributed, the RDA is set at 2 standard deviations (SD) above the EAR:
RDA = EAR + 2 SDEAR.
If the SDs reported in studies are inconsistent, or if sufficient data on variation in requirements are not available for other reasons, a standard estimate of variance will be applied. This estimate assumes
It is recognized that the definition of EAR implies a median as opposed to a mean or average. The median and average would be the same if the distribution of requirements followed a symmetrical distribution, and would diverge as a distribution became skewed. Three considerations prompted the choice of the term estimated average requirement: (1) data are rarely adequate to determine the distribution of requirements, (2) precedent has been set by other countries that have used the same term for reference values similarly derived (COMA, 1991), and (3) the impreciseness of the data evaluated makes the determination of a statistically reliable median extremely unlikely.