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DRI DIETARY REFERENCE INTAKES: Applications in Dietary Assessment
daily intakes for an individual are typically not available to reliably estimate the day-to-day variability, the pooled day-to-day SD of intake from CSFII (see Table B-2, Table B-3, Table B-4 through Table B-5) or from NHANES is used.
The z-statistic is constructed as follows:
z = × (observed mean intake − AI)/SD of daily intake.
By rearrangement, this can also be expressed as:
z = (observed mean intake − AI) / (SD of daily intake/ ).
The z-statistic is then compared to tabulated values (a selection of which are presented in Table B-6), to decide whether the desired level of accuracy is achieved when stating that the usual intake is larger than the AI.
For example, consider a nutrient such as calcium with an AI of 1,000 mg /day, and suppose that the SD of daily intake from CSFII for the appropriate life stage and gender group is 325 mg/day.
TABLE B-6 Selected Values of z and the Associated Level of Confidence When Concluding That Individual Usual Intake Is Larger Than the Adequate Intake (AI) or Less Than the Tolerable Upper Intake Level (UL)