New nonparametric confidence intervals for the Youden index

The Youden index, a main summary index for the receiver operating characteristic (ROC) curve, is a comprehensive measurement for the effectiveness of a diagnostic test. For a continuous-scale diagnostic test, the optimal cut point for positive disease is the cut point leading to the maximization of the sum of sensitivity and specificity. Finding the Youden index of the test is equivalent to maximize the sum of sensitivity and specificity for all the possible values of the cut point. In this paper, we propose new nonparametric confidence intervals for the Youden index. Extensive simulation studies are conducted to compare the relative performance of the new intervals with the existing parametric interval for the index. Our simulation results indicate that the newly developed nonparametric intervals are competitive with the existing parametric interval when the underlying distributions are correctly specified, and they outperform the existing parametric interval when the underlying distributions are misspecified. The new intervals are robust and easy to implement in practice. A real example is also used to illustrate the application of the proposed intervals.