If data about variability in requirements are insufficient to calculate an SD, a coefficient of variation (CV EAR) of 10 percent will ordinarily be assumed and used in place of the SD. Because
CV EAR = SD EAR /EAR, and
SD = (EAR × CV EAR);
the resulting equation for the RDA is
RDA = EAR + 2 (0.1 × EAR), or
RDA = 1.2 × EAR.
If the nutrient requirement is known to be skewed for a population, other approaches will be used to find the ninety-seventh to ninety-eighth percentile to set the RDA.
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 expenditure of many individuals residing in Canada