A sequential design is proposed to test whether the accuracy of a binary diagnostic biomarker meets the minimal level of acceptance. The accuracy of a binary diagnostic biomarker is a linear combination of the marker's sensitivity and specificity. The objective of the sequential method is to minimize the maximum expected sample size under the null hypothesis that the marker's accuracy is below the minimal level of acceptance. The exact results of two-stage designs based on Youden's index and efficiency indicate that the maximum expected sample sizes are smaller than the sample sizes of the fixed designs. Exact methods are also developed for estimation, confidence interval and p-value concerning the proposed accuracy index upon termination of the sequential testing. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.
Keywords: Youden's index; expected sample size; inference upon early stopping; sensitivity; sequential testing; specificity; two-stage designs; type I error.
Published 2016. This article is a U.S. Government work and is in the public domain in the USA.