Tail-adaptive Bayesian shrinkage

Modern genomic studies are increasingly focused on discovering more and more interesting genes associated with a health response. Traditional shrinkage priors are primarily designed to detect a handful of signals from tens and thousands of predictors. Under diverse sparsity regimes, the nature of signal detection is associated with a tail behaviour of a prior. A desirable tail behaviour is called tail-adaptive shrinkage property where tail-heaviness of a prior gets adaptively larger (or smaller) as a sparsity level increases (or decreases) to accommodate more (or less) signals. We propose a global-local-tail (GLT) Gaussian mixture distribution to ensure this property and provide accurate inference under diverse sparsity regimes. Incorporating a peaks-over-threshold method in extreme value theory, we develop an automated tail learning algorithm for the GLT prior. We compare the performance of the GLT prior to the Horseshoe in two gene expression datasets and numerical examples. Results suggest that varying tail rule is advantageous over fixed tail rule under diverse sparsity domains.