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## Dietary Reference Intakes: Applications in Dietary Assessment (2000) Institute of Medicine (IOM)

### Citation Manager

. "Appendix B: Nutrient Assessment of Individuals: Statistical Foundations." Dietary Reference Intakes: Applications in Dietary Assessment. Washington, DC: The National Academies Press, 2000.

 Page 200

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DRI DIETARY REFERENCE INTAKES: Applications in Dietary Assessment

Given five individuals, each with three days of intake records and observed mean intakes of 1,050, 1,150, 1,200, and 1,250 mg/day, respectively, what can be determined about the adequacy of their usual intakes? Assume that, to determine if the usual intake is higher than the AI, a minimum confidence level of 85 percent is desired.

To calculate the z-values for each of the five individuals, first divide the SD of daily intake by the (as 3 daily records are available for each). In this example, 325/ equals 188. The z-values are now computed as (observed mean intake − AI)/188. For the five individuals, the corresponding z-values are 0.27, 0.53, 0.80, 1.07, and 1.33, respectively. From a standard z-table the probabilities of correctly concluding that the usual intake is larger than the AI for each of the five individuals are 61, 70, 79, 86, and 91 percent, respectively. Only for the last two individuals, with observed mean intakes of 1,200 and 1,250 mg /day, would there be an 85 percent confidence level when stating that usual intakes are greater than 1,000 mg/day.

The value of the z-statistic will increase whenever

• the difference between the observed mean intake and the AI increases;

• the SD of daily intake for the nutrient is low; and

• the number of days of intake data available for the individual increases.

This z-test relies on the assumption of normality of daily intakes. For nutrients such as vitamin A, vitamin B12, and others with a CV of daily intake larger than 60 to 70 percent, this test is likely to perform poorly. While the calculations are still possible, the level of assurance resulting from the test will be incorrect. The performance of the test also depends on accurately estimating the day-to-day variability in intakes for the individual. It is suggested that the pooled SD of daily intake obtained, for example, from Table B-2, Table B-3, Table B-4 through Table B-5 be used in the calculations even though it is likely to be a poor estimate of the individual's true day-to-day variability in intakes. As stated earlier, a more justifiable alternative cannot be offered at this time, as no extensive studies on the dependence of individual SD of intake and individual mean intake have been published. More research is needed in this area.

 Page 200
 Front Matter (R1-R14) Contents (R15-R18) Summary (1-18) I. Historical Perspective and Background (19-20) 1 Introduction and Background (21-28) 2 Current Uses of Dietary Reference Standards (29-42) II. Application of DRIs for Individual Diet Assessment (43-44) 3 Using Dietary Reference Intakes for Nutrient Assessment of Individuals (45-70) III. Application of DRIs for Group Diet Assessment (71-72) 4 Using the Estimated Average Requirement for Nutrient Assessment of Groups (73-105) 5 Using the Adequate Intake for Nutrient Assessment of Groups (106-112) 6 Using the Tolerable Upper Intake Level for Nutrient Assessment of Groups (113-126) 7 Specific Applications: Assessing Nutrient Intakes of Groups Using the Dietary Reference Intakes (127-144) IV. Fine-Tuning Dietary Assessment Using the DRIs (145-146) 8 Minimizing Potential Errors in Assessing Group and Individual Intakes (147-161) 9 Research Recommended to Improve the Uses of Dietary Reference Intakes (162-167) 10 References (168-178) Appendix A: Origin and Framework of the Development of Dietary Reference Intakes (179-184) Appendix B: Nutrient Assessment of Individuals: Statistical Foundations (185-202) Appendix C: Assessing Prevalence of Inadequate Intakes for Groups: Statistical Foundations (203-210) Appendix D: Assessing the Performance of the EAR Cut-Point Method for Estimating Prevalence (211-231) Appendix E: Units of Observation: Assessing Nutrient Adequacy Using Household and Population Data (232-238) Appendix F: Rationale for Setting Adequate Intakes (239-253) Appendix G: Glossary and Abbreviations (254-261) Appendix H: Biographical Sketches of Subcommittee Members (262-266) Index (267-281) Summary Table: Estimated Average Requirements (282-283) Summary Table: Tolerable Upper Intake Levels (284-286) Summary Table: Recommended Intakes for Individuals (287-289)