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

### Citation Manager

. "8 Minimizing Potential Errors in Assessing Group and Individual Intakes." Dietary Reference Intakes: Applications in Dietary Assessment. Washington, DC: The National Academies Press, 2000.

 Page 159

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DRI DIETARY REFERENCE INTAKES: Applications in Dietary Assessment

is uncertainty associated with them and this uncertainty can, in principle, be reflected in a standard deviation for the prevalence. Uncertainty in the prevalence estimates can come from three sources: sampling variability, variability associated with the EAR, and variability associated with collection of intake data.

###### Sampling Variability

Any time a sample of individuals is used to make inferences about a larger group, a statistical error (often called sampling variability) is incurred. In the case of dietary assessment, not only are the intake data obtained for just a sample of individuals in the group, but also the sample of intake days is small for each of those individuals. Therefore, two sources of sampling variability are immediately identifiable —one arising from not observing the entire population and one arising from not observing intake on all days for each individual.

Statistical techniques can be used to estimate the amount of sampling variability associated with prevalence estimates, although the computations are complex. When standard deviations can be calculated, it is appropriate to report not only the prevalence estimate but also its standard deviation. For example, for group X the prevalence of inadequate intake of nutrient Y was a percent ± b percent, where a is the estimated percent prevalence of nutrient inadequacy and b is the standard deviation of the prevalence estimate. When b is small relative to a, the prevalence has been estimated with a good degree of accuracy.

An additional consideration when determining the sampling variability is the effect of the survey design. Dietary intake data are typically collected in complex surveys, and thus the survey design must be taken into account when estimating standard deviations. Additional information on the estimation of standard deviations under complex survey designs, or in particular, about the estimation of standard deviations for prevalence estimates can be found in Nusser et al. (1996) and Wolter (1985).

###### Variability Associated with the EAR

Variability associated with the EAR may increase the uncertainty around prevalence estimates. Both the probability approach and the cut-point method use the EAR when estimating prevalence of inadequacy. However, the EAR is itself an estimate, and thus has its own uncertainty. Practical statistical approaches have not yet been developed for combining the two uncertainties—those around intake

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 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)