Cover Image

PAPERBACK
$34.95



View/Hide Left Panel

Box D-3 Major findings—Distribution of requirements not symmetrical

  • The bias in the estimate of inadequacy that results from application of the EAR cut-point method when the distribution of requirements is skewed can be severe.

  • When skewness exceeds values around 2, the relative bias (estimated prevalence/true prevalence) is very large—over 100 percent.

  • Even though this simulation was limited in scope, results are striking enough for the Uses Subcommittee to recommend that the EAR cut-point method not be used to assess the prevalence of nutrient inadequacy for a nutrient with a skewed requirement distribution.

of 50,000, prevalence of inadequacy was estimated from the population itself. Therefore, the values shown in Table D-1 and in Figure D-19 represent the actual proportion of individuals with intakes below requirements (true prevalence) and the estimate obtained from application of the EAR cut-point method.

The only nutrient for which there is strong evidence indicating a skewed requirement distribution (at the time this report was published) is iron in menstruating women (FAO/WHO, 1988). In recent Institute of Medicine reports on Dietary Reference Intakes (DRIs)

TABLE D-1 True Prevalence of Inadequacy and Estimated Prevalence of Inadequacy of Iron Obtained Using the EAR Cut-point Method

Distribution of Requirements

 

Mean

Standard Deviation

Skewness

True Prevalence (%)

Estimated Prevalence (%)

Bias (%)

8.4

0.7

0.62

12

11

1

8.6

1.4

1.32

15

11

4

9.0

2.5

2.51

20

11

9

9.5

3.9

3.15

24

11

13

10.4

6.9

5.73

28

12

16

NOTE: The distribution of usual intakes is fixed to be normal with a mean of 12 mg and a standard deviation of 3 mg.



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement