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DRI DIETARY REFERENCE INTAKES: Applications in Dietary Assessment
the SD of requirement. Since the SD of requirement is an important component of the SDD, an inaccurate value for the SD of requirement will result in an inaccurate value for SDD and hence the ratio of D/SDD.
The SD of daily intake for the individual is considerably larger (or smaller) than the pooled SD of daily intake obtained from CSFII (or from the National Health and Nutrition Examination Survey).
The individual's intake is underreported, so that the mean observed intake is a biased estimator of the individual's usual intake.
The described approach should not be used in isolation from other information available to nutrition professionals. Most professionals combine the nutrient intake data with other sources of information such as food guides and answers to questions about whether intake was typical or atypical.
This statistical approach to individual assessment is based on quantitative dietary records and recalls, where the method for deriving the error term (the within-person standard deviation of intakes) is known and easy to apply. Many researchers and health professionals use other methods of estimating usual intakes, such as food frequencies or diet histories, or a combination of various methods. With alternative assessment methodologies, the overall objective of the assessment remains the same—to determine whether usual intake by the individual exceeds the individual's requirement—and professionals must rely on estimates of both usual intake and requirement. The important consideration is that different methodologies for determining dietary intake have different sources and magnitudes of random error in estimating usual intake—the equivalent of the within-person standard deviation of intake discussed above—and may not provide adequate quantitative estimates of total nutrient intake over the period of observation. Additional discussion of dietary intake measurement instruments is provided in Chapter 8. However, a detailed discussion of these methods is beyond the scope of this report, and users will need to turn to other sources to find estimates of the error associated with alternative methods for estimating usual intake.
Using the AI
If an AI must be used to interpret dietary intake data because an EAR has not been set, the process described above cannot be used in the same way. Before discussing a statistical approach to individual assessment for nutrients with an AI, it is critical to emphasize the