is sometimes of interest to compare population-level consumption data (such as food disappearance data for a country) with a requirement estimate. Appropriate ways to make such comparisons are also discussed in Appendix E. However, the methods involve many assumptions, and errors may be large.

Deriving nutrient intake data from dietary intake data requires the use of a food composition database. Accuracy of the food composition data and the software to access it are critical for assessments of dietary adequacy. Nutrient databases need to be kept current and contain data on dietary supplements. In the United States and Canada the primary sources of nutrient composition data are the U.S. Department of Agriculture Nutrient Database for Standard Reference, Release 13 and its revisions (USDA, 1999; Watt et al., 1963).

Databases should be evaluated for the number of food items included that are relevant to the population under study (Kuhnlein and Soueida, 1992; Smith et al., 1991b). The currency of data for foods derived from recipes is important; they should reflect changes in fortification levels of primary ingredients. Ideally, the database should not have missing values, and values calculated from similar food items should be identified (Buzzard et al., 1991; Juni, 1996; Nieman et al., 1992).

Other considerations when evaluating databases include whether the values are for food as consumed (rather than as purchased); nutrient analytical methodology used, including extent of sampling required and feasibility of addressing variability in nutrient content; and conventions and modes of data expression (Greenfield and Southgate, 1992; Rand et al., 1991).

When accurate food consumption data are not available, it may be more meaningful to compare food intake to food-based dietary standards (such as the Food Guide Pyramid [USDA, 1992]) than to compare nutrient intake to the DRIs.

For nutrients with a wide range of biological availability in food, a population's prevalence of inadequate intakes will be inaccurately estimated if the average bioavailability for foods chosen by individuals in the population differs from the bioavailability assumed when setting the Estimated Average Requirement (EAR). The distribution