97.5 percent) that an observed intake is below an individual's requirement, it is necessary to have either a large number of days of intake or for the intake to be substantially below the EAR. Taking magnesium for women 19 through 50 years of age as an example, with 7 days of observed intake, an intake of about 180 mg/day (compared with the EAR of 265 mg/day) would have a high probability (97.5 percent) of being below an individual's requirement. However, it is often the case that a nutrition professional wants to have a high level of confidence when concluding that intakes are adequate but will find a much lower level of confidence acceptable when concluding that intake is inadequate. For example, even if the probability of inadequacy was only 50 percent, most professionals would urge a client to try to increase intake of that nutrient. One would want to be much more certain before concluding that a client's intake was adequate and that no action to improve intake was needed.
Thus, for practical purposes, many users of the DRIs may find it useful to consider that observed intakes below the EAR very likely need to be improved (because the probability of adequacy is 50 percent or less), and those between the EAR and the RDA probably need to be improved (because the probability of adequacy is less than 97.5 percent). Only if intakes have been observed for a large number of days and are at or above the RDA, or observed intakes for fewer days are well above the RDA, should one have a high level of confidence that the intake is adequate. It is hoped that computer software will be developed that will compute these probabilities (as described in Appendix B), thus offering more objective alternatives when individual intakes are evaluated.
In summary, for nutrients for which an EAR has been established, it is possible to assess the adequacy of an individual's usual intake for a nutrient. The approach described above takes into account the uncertainty about the true value of the individual's usual intake, and also the uncertainty about the individual's requirement for the nutrient. The method cannot be employed when the distribution of requirements for the nutrient is skewed (as in the case of iron requirements for menstruating women), or when the distribution of daily intakes for an individual is not normal (as is the case with nutrients for which the CV of intake has been calculated to be above 60 to 70 percent, see Appendix Table B-2, Table B-3, Table B-4 through Table B-5). There are three additional sources of potentially large error when using this approach to assessing an individual's intake:
The assumed 10 percent CV estimate applied to many nutrients to date (IOM, 1997, 1998b, 2000) may not be a reliable estimator of