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TABLE B-1 Values for the Ratio D/SDD and Corresponding Probability of Correctly Concluding that Usual Intake Is Adequate or Inadequate

Criterion

Conclusion

Probability of Correct Conclusion

D/SDD> 2.00

Usual intake is adequate

0.98

D/SDD> 1.65

Usual intake is adequate

0.95

D/SDD> 1.50

Usual intake is adequate

0.93

D/SDD> 1.00

Usual intake is adequate

0.85

D/SDD> 0.50

Usual intake is adequate

0.70

D/SDD> 0.00

Usual intake is adequate (inadequate)

0.50

D/SDD< −0.50

Usual intake is inadequate

0.70

D/SDD< −1.00

Usual intake is inadequate

0.85

D/SDD< −1.50

Usual intake is inadequate

0.93

D/SDD< −1.65

Usual intake is inadequate

0.95

D/SDD< −2.00

Usual intake is inadequate

0.98

SOURCE: Adapted from Snedecor and Cochran (1980).

and is only approximate. The assumptions that are implicit in the criterion include:

  1. The distribution of daily intakes Y around the mean intake is approximately normal, or at least symmetrical, for the individual. Any nutrient with a skewed distribution of daily intakes would not satisfy this assumption, such as those nutrients in Table B-2, Table B-3, Table B-4 through Table B-5 with a CV larger than about 60 to 70 percent.

  2. The distribution of requirements in the group is approximately normal.

  3. The daily intake Y accurately reflects the individual's true intake of the nutrient for the day.

  4. A reliable estimate of the day-to-day variability in intake for the individual is available.

  5. Intakes are independent of requirements.

In probabilistic terms, the value of 1 for the ratio D/SDD corresponds to an approximate 0.15 p-value for the test of the hypothesis that y > ρ. That is, when it is concluded that intake is adequate, there is approximately an 85 percent chance of reaching the correct conclusion and approximately a 15 percent chance of making a mistake (erroneously concluding that intake is adequate). Because the criterion is formulated on this probabilistic basis, the level of



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