WIC eligibility. To use a dietary method to assess an individual’s dietary risk of failure to meet Dietary Guidelines or inadequate intake, the method must have acceptable performance characteristics (described in Chapter 4). The committee focused on available dietary tools with regard to their ability to estimate usual intake and their performance characteristics (validity, reliability, measurement error, bias, and misclassification error). The intent was to determine how well the tools could identify an individual’s WIC eligibility status based on the dietary risk of failure to meet Dietary Guidelines or inadequate intake. The committee considered data related to the correct identification of intakes of nutrients, foods, and food groups since elements from any of these three groupings could be used as the indicator on which a criterion could be based. For example, a method to identify failure to meet Dietary Guidelines must be able to identify accurately a person’s usual intake from each of the five basic food groups of the Food Guide Pyramid.
This chapter describes (1) the importance of assessing usual intake, (2) commonly used research-quality dietary assessment methods, including their strengths and limitations, (3) methods that compare food intakes with the Dietary Guidelines, and (4) conclusions about food-based methods for eligibility determination.
As explained below, dietary assessment for the purpose of determining WIC eligibility must be based on long-term intake or the usual pattern of dietary intake, rather than intake reported for a single day or a few days. In the United States and other developed countries, a person’s dietary intake varies substantially from day to day (Basiotis et al., 1987; Carriquiry, 1999; IOM, 2000a; Nelson et al., 1989; Tarasuk, 1996; Tarasuk and Beaton, 1999). This variation introduces random error in estimates of usual intake. Day-to-day variation in intake arises from multiple biologic and environmental influences such as appetite, physical activity, illness, season of the year, holidays, and personal economic conditions. An individual’s intake may become either more erratic or more monotonous when economic constraints are added to other influences on dietary intake.
Figure 5-1 presents distributions of intake for a hypothetical nutrient X that is normally distributed. It depicts the relationship between the distributions of usual intakes of individuals within a population and the distribution of usual intake for that population (solid line P). L marks the cut-off point for determining whether an individual’s usual intake is above or below a specified cut-off