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Activity Number: 684
Type: Contributed
Date/Time: Thursday, August 8, 2013 : 10:30 AM to 12:20 PM
Sponsor: Biometrics Section
Abstract - #309539
Title: Estimation and Evaluation of Optimal Thresholds for the Believe the Positive Sequential Testing Strategy
Author(s): Amber Wilk and Donna McClish*+
Companies: VCU and VCU
Keywords: sequential testing ; Believe the Positive (BP) ; Generalized Youden Index (GYI) ; optimal threshold
Abstract:

Many continuous medical tests rely on a threshold for diagnosis. A sequential testing strategy, called Believe the Positive, classifies a patient positive if either the first test is greater than a threshold, ?1 or negative on the first test and greater than ?2 on the second test. A threshold pair ?*= (?1,?2) was defined as optimal if it maximized GYI=Sensitivity(Se) + r*(Specificity(Sp) - 1). Formulas were derived to estimate ?* assuming tests follow a binormal distribution, using the Newton-Raphson algorithm. A simulation study was performed assessing bias, root mean square error (RMSE), percentage of under/over estimation of Se/Sp, and coverage of simultaneous confidence intervals (SCI)/ellipses. When the area under the curve(AUC) between tests is equal, median RMSE and median bias in Se and Sp decrease and the coverage of the SCI and confidence ellipses improve as sample size, AUC, and the ratio of standard deviations of each group increase. This also holds true for percentage of overestimation of Se and Sp except when the allocation between groups favors those without disease. This method is an improvement over an empirical estimate.


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