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of interest. These univariate distributions can be combined and the prevalence of inadequate nutrient intakes can be estimated statistically by using the probability approach (NRC, 1986).

The probability approach relates individual intakes to the distribution of requirements. The probability approach applies a continuous risk-probability function to each individual's estimated intake and then averages the individual probabilities across the population or group. The first step in applying the probability approach is to construct a risk curve using the information on the requirement distribution of the group (median and variance). The risk curve specifies the probability that any given intake is inadequate for the individual consuming that intake. Figure 4-3 shows an example of a risk curve. An intake at the level of the average requirement has a probability of inadequacy of approximately 50 percent for all nutrients whose requirements follow a normal distribution.

The risk curve in Figure 4-3 is from a hypothetical nutrient requirement distribution. For simplicity, the requirements are normally distributed and the mean requirement is 100 units. Intake less than 50 units is associated with 100 percent risk of inadequacy whereas

FIGURE 4-3 Risk curve from a normal requirement distribution having a mean of 100 units. Intakes less than 50 units are associated with 100 percent risk of inadequacy while intakes above 150 units have 0 percent risk of inadequacy. Intake equal to the mean requirement of 100 units has a 50 percent risk of inadequacy (the definition of the Estimated Average Requirement [EAR]).

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