dietary recall data are available for a subsample of individuals, with one day of recall data available for the remainder of the sample.
Thus, to conduct evaluations of dietary survey data, it is usually necessary first to adjust the intake distributions based on at least two nonconsecutive days of dietary recalls to obtain the usual nutrient intake distribution. If these adjustments are not made, outcome variables that rely on any measure other than the group's mean intake are biased (Carriquiry et al., 1997; Nusser et al., 1996). For example, the percentage of individuals in a group with intakes less than a specified cutoff level would be biased (either over- or under-estimated) if determined from unadjusted data on nutrient intakes. See Chapter 4 for methods to adjust intake distributions.
What are the characteristics of the distributions of usual nutrient intake? How variable are usual intakes?
Data available: 24-hour dietary recall data on a nationally representative sample of individuals, with two or more nonconsecutive days of data collected for at least a subsample of individuals.
This discussion assumes that dietary recall data are available from a nationally representative sample of individuals and have been used to estimate the usual nutrient intakes of the population from food and supplements.
The following summary descriptive measures could be examined: mean, median, and other percentiles of the usual nutrient intake distribution. An example of appropriate descriptive statistics is given in Table 7-1.
Many researchers have expressed intakes as a percentage of the Recommended Dietary Allowance (RDA) primarily to aid the interpretation of descriptive statistics across life stage and gender groups that have different requirements. Although expressing mean intake as a percentage of the RDA is not incorrect, it is easily misinterpreted. These statistics cannot be used to assess nutrient adequacy.