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True prevalence

The actual prevalence of a condition assuming no error in measurement of either requirements or intakes that would result in false negative or false positive classifications.


Uncertainty factor; a value assigned to a specific nutrient reflecting the level of uncertainty about data used to establish a Tolerable Upper Intake Level.


Tolerable Upper Intake Level; the highest average daily nutrient intake level likely to pose no risk of adverse health effects to almost all individuals in the general population. As intake increases above the UL, the potential risk of adverse effects increases.

Unit of observation

The level of aggregation at which data are collected. For example, the unit of observation for dietary assessment may be the individual, the household, or the population.

Univariate distribution

The distribution of a single variable.

Usual intake

The long-run average intake of food, nutrients, or a specific nutrient for an individual.

Variance of usual intakes or requirements

In the statistical sense, reflects the spread of the distribution of usual intakes or requirements on both sides of the mean intake or requirement. When the variance of a distribution is low, the likelihood of seeing values that are far away from the mean is low; in contrast, when the variance is large, the likelihood of seeing values that are far away from the mean is high. For usual intakes and requirements, variance reflects the person-to-person variability in the group.

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