Tail Risk in the Tail: Estimating High Quantiles When a Related Variable is Extreme

In this article we address the problem of high quantile estimation conditional on a related variable being extreme. The problem set-up is of interest in a number applications to evaluate tail risk of a focal variable in the tail of a conditioning variable. A primary example we consider is the assessment of systemic risk in financial markets using a risk measure known as the conditional value-at-risk (CoVaR). The proposed estimator is based on a novel approach to handle the bivariate tail dependence structure through an adjustment factor that can be used in conjunction with univariate high quantile estimation techniques. We establish the asymptotic behavior of the estimator under relatively weak assumptions, and illustrate its performance via simulation studies and a real data example. Supplementary materials for this article are available online, including a standardized description of the materials available for reproducing the work.