Box D-1Major findings—Intakes and requirements are correlated
When the SD_{r} is small relative to the SD_{i}, no serious biases on the estimate of prevalence are evident even at correlation values as high as 0.5 or 0.6 (Figure D-1 and Figure D-4).
When the SD_{r} increases relative to the SD_{i}, increasing the correlation between intakes and requirement can result in noticeable biases in the prevalence of inadequacy even when the correlation is no larger than about 0.4 (Figure D-2 and Figure D-5).
When the SD_{r} is as large as the SD_{i}, the bias in the estimate of prevalence can be significant even if the correlation between intakes and requirements is 0. This indicates that the EAR cut-point method is less robust to departures from the last assumption (variance of requirements must be smaller than variance of usual intake) (Figure D-3 and Figure D-6).
When mean intake is equal to the EAR (prevalence is exactly equal to 50 percent), neither increasing the correlation coefficient to 1 nor equating the variances of requirements and intakes introduces a bias in the estimated prevalence (Figure D-7, Figure D-8, and Figure D-9).
FIGURE D-1 The effect of correlation between usual intake and requirement on the prevalence of inadequate intakes estimated using the Estimated Average Requirement (EAR) cut-point method for 10 values of the correlation. For all correlations, mean intake = 90, standard deviation (SD) of intake = 30, EAR = 55, and SD of requirement = 7.5 units.
NOTE: When the SD of requirement is small relative to the SD of intake, there is no serious bias of the EAR cut-point method until correlation reaches 0.5 to 0.6.
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Appendix D: Assessing the Performance of the EAR Cut-Point Method for Estimating Prevalence ."
Dietary Reference Intakes: Applications in Dietary Assessment . Washington, DC: The National Academies Press,
2000 .
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