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Appendix B: Nutrient Assessment of Individuals: Statistical Foundations
Pages 185-202

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From page 185...
... Similarly, guidance on how to determine, for a given confidence level, whether an incliviclual's usual intake exceeds the Adequate Intake (AI) or the Tolerable Upper Intake Level (UL)
From page 186...
... The standard deviation of requirements in the population, clenoteci by SDr, is proportional to the uncertainty about how precisely r estimates p. If every incliviclual haci the exact same requirement for the nutrient, then r (which is set to be equal to the EAR)
From page 187...
... Conversely, if D is a large negative number, then it is likely that p is larger than y and that the individual's intake is not adequate. The obvious question to be posed is, How large would D have to be before it can be conclucleci, with some degree of assurance, that the unobservable usual intake is larger than the unobservable requirement?
From page 188...
... As the number (n) of clays of intake available on the incliviclual increases, the variance of the observed mean intake should decrease (i.e., the accuracy of the estimate for y increases)
From page 189...
... In other words, it is reasonably certain that the unobservable true difference between the incliviclual's usual intake and requirement (y - pJ is positive and thus the incliviclual's usual intake exceeds requirement. · If D/SDD is less than -1, then it is reasonably certain that the incliviclual's usual intake is inacloquate.
From page 190...
... The assumptions that are implicit in the criterion include: 1. The distribution of ciaily intakes Yarounci the mean intake y is approximately normal, or at least symmetrical, for the incliviclual.
From page 191...
... 851 38 1,147 36 723 31 922 31 NOTE: When the CVis larger than 60 to 70 percent the distribution of daily intakes is nonnormal and the methods presented here are unreliable. a Square root of the residual variance after accounting for subject, and sequence of observation (gender and age controlled by classifications)
From page 192...
... Note that D/SDD clepencis on the size of the difference between observed mean intake and the EAR and the standard deviation of that difference. For very large differences between observed mean intake and the EAR, it is likely that the ratio will exceed 1 and usual intake exceeds requirement.
From page 193...
... C Sample size was inadequate to provide separate estimates for pregnant or lactating women. SOURCE: Data from Continuing Survey of Food Intakes by Individuals 1994-1996.
From page 194...
... 145 72 199 71 129 70 137 66 NOTE: When the CVis larger than 60 to 70 percent the distribution of daily intakes is nonnormal and the methods presented here are unreliable. a Square root of the residual variance after accounting for subject, and sequence of observation (gender and age controlled by classifications)
From page 195...
... Other estimates have been clevelopeci from research databases and from large survey ciata sets with replicate observations (e.g., the Continuing Survey of Food Intakes by Inclivicluals tCSFII]
From page 196...
... Suppose that the CVof intake was 60 percent, then the SD of intake is 0.6 x mean intake. If 2 SDs of intake are now subtracted from the incliviclual's mean intake a negative value is obtained, inclicating that the distribution of observed intakes around the incliviclual's usual intake is not normal.
From page 197...
... Incorrect Specification of the SD of Requirement Until now, little if any attention has been paid to reliably estimating the variance of nutrient requirement distributions. DRI reports (IOM, 1997, 1998b, 2000)
From page 198...
... A simple z-test to decide whether an individual's unobservable usual intake is larger than the AI can be used. The test assumes that daily intakes for an individual have a distribution that is approximately normal around the individual's usual intake.
From page 199...
... /8D of ciaily intake. By rearrangement, this can also be expressed as: z = (observed mean intake - AI)
From page 200...
... From a stanciarci z-table the probabilities of correctly concluding that the usual intake is larger than the AI for each of the five inclivicluals are 61, 70, 79, 86, and 91 percent, respectively. Only for the last two inclivicluals, with observed mean intakes of 1,200 and 1,250 mg /clay, would there be an 85 percent confidence level when stating that usual intakes are greater than 1,000 mg/ciay.
From page 201...
... Because usual intakes are unobservable, the uncertainty of how well observed mean intake estimates usual intake must be accounted for, similar to comparing intake to the Acloquate Intake (AI) as cliscusseci in the previous section.
From page 202...
... For other nutrients, ULs refer only to nutrient intake from food fortificants, supplements, and pharmacological products. In these cases, the proposed methods are even less reliable, as currently there are no estimates of the within-person stanciarci deviation of intakes from supplement use alone.


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