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Appendix D
Definitions of Yield and Sensitivity of Cutoff Points for Nutrition Risk
Efficacy of WIC interventions: the proportion of individuals selected for WIC whose bad outcomes will be prevented or reduced =
where
Y = those identified who have the risk and will benefit
w = those identified who have the risk and will not benefit
Overall benefit from WIC
Identified by criterion
Yes
No
Yes
Y
w
Yield of risk1: the proportion of those identified at risk who are at risk =
where
B = those identified at risk who are at risk
o = those identified at risk who are not at risk
1
Yield of risk is called positive predictive value in epidemiology (Last, 1988).
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At risk of bad outcome
Identified by criterion
Yes
No
Yes
B
o
No
b
O
Not all those who have the risk and are identified at risk (B) will benefit, thus:
Combining equations D-2 and D-3:
Yield of benefit: proportion of those identified at risk who will benefit =
Sensitivity for risk2 = Sensitivity for benefit:
References
Habicht, J-P. 1980. Some characteristics of indicators of nutritional status for use in screening and surveillance. Am. J. Clin. Nutr. 33:531-535.
Habicht, J-P., L.D. Meyers, and C. Brownie. 1982. Indicators for identifying and counting the improperly nourished. Am. J. Clin. Nutr. 35:1241-1254.
Last, J.M. 1988. A Dictionary of Epidemiology. London: Oxford University Press.
2
Nutritional examples of tradeoffs between specificity and sensitivity are discussed in Habicht (1982), and the relationship of specificity-sensitivity tradeoffs to the positive predictive value are discussed in Habicht (1980).
Representative terms from entire chapter:
predictive value
