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FIGURE D-9 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 = 90, and SD of requirement = 30 units.

NOTE: When mean intake is equal to the EAR (prevalence of inadequate intakes is 50 percent), a variance of requirement as large as the variance of intake introduces no bias in the prevalence estimate using the EAR cut-point method.

Figure D-10, Figure D-11, and Figure D-12 show the bias of the prevalence estimates obtained from application of the EAR cut-point method relative to the true prevalence. The bias is calculated as the difference between the average prevalence estimate over the 200 replicates, and the true prevalence in the group. These three figures summarize the results presented in Figure D-1, Figure D-2, Figure D-3, Figure D-4, Figure D-5, Figure D-6, Figure D-7, Figure D-8 through Figure D-9.

In Figure D-10 the solid line and dots represents the bias in the estimated prevalence at various levels of the correlation between intakes and requirements for the case where the EAR is 55 units and the SDr is 7.5. The dotted line and squares represents the bias of the EAR cut-point prevalence estimate when the SDr is increased to 15 units. Finally, the dashed line and stars shows the amount of bias in the EAR cut-point prevalence estimates when the SDr is equal to the SDi of 30 units. Notice that when SDr is small, the bias in the prevalence estimate is small, even at very high values of the correlation

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