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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OCR for page 359
--> 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).

OCR for page 359
-->   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).