title: Optimal cut-point and its corresponding Youden Index to discriminate individuals using pooled blood samples.
abstract: Costs can hamper the evaluation of the effectiveness of new biomarkers. Analysis of smaller numbers of pooled specimens has been shown to be a useful cost-cutting technique. The Youden index (J), a function of sensitivity (q) and specificity (p), is a commonly used measure of overall diagnostic effectiveness. More importantly, J is the maximum vertical distance or difference between the ROC curve and the diagonal or chance line; it occurs at the cut-point that optimizes the biomarker's differentiating ability when equal weight is given to sensitivity and specificity. Using the additive property of the gamma and normal distributions, we present a method to estimate the Youden index and the optimal cut-point, and extend its applications to pooled samples. We study the effect of pooling when only a fixed number of individuals are available for testing, and pooling is carried out to save on the number of assays. We measure loss of information by the change in root mean squared error of the estimates of the optimal cut-point and the Youden index, and we study the extent of this loss via a simulation study. In conclusion, pooling can result in a substantial cost reduction while preserving the effectiveness of estimators, especially when the pool size is not very large.
authors.affiliation: Division of Epidemiology, Statistics and Prevention Research, National Institute of Child Health and Human Development, National Institutes of Health, DHHS, Bethesda, Maryland, USA. schistee@mail.nih.gov
authors.forename: Enrique F
authors.initials: EF
authors.lastname: Schisterman
authors.forename: Neil J
authors.initials: NJ
authors.lastname: Perkins
authors.forename: Aiyi
authors.initials: A
authors.lastname: Liu
authors.forename: Howard
authors.initials: H
authors.lastname: Bondell
mesh_terms: D000465:Algorithms; D015415:Biomarkers / Q000097:blood*; D003365:Costs and Cost Analysis; D006801:Humans; D008403:Mass Screening / Q000191:economics / Q000592:standards* / Q000706:statistics & numerical data; D012372:ROC Curve; D018401:Sample Size; D012494:Sampling Studies; D015983:Selection Bias; D012680:Sensitivity and Specificity
chemical_list: D015415:Biomarkers