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Paper No. 14-10

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D Rossell and D Telesca

Non-Local Priors for High-Dimensional Estimation

Abstract: Simultaneously achieving parsimony and good predictive power in high dimensions is a main challenge in statistics. Non-local priors (NLPs) possess appealing properties for high-dimensional model choice. but their use for estimation has not been studied in detail, mostly due to difficulties in characterizing the posterior on the parameter space. We give a general representation of NLPs as mixtures of truncated distributions. This enables simple posterior sampling and flexibly defining NLPs beyond previously proposed families. We develop posterior sampling algorithms and assess performance in p >> n setups. We observed low posterior serial correlation and notable high-dimensional estimation for linear models. Relative to benchmark and hyper-g priors, SCAD and LASSO, combining NLPs with Bayesian model averaging provided substantially lower estimation error when p >> n. In gene expression data they achieved higher cross-validated R2 by using an order of magnitude less predictors than competing methods. Remarkably, these results were obtained without the need for methods to pre-screen predictors. Our findings contribute to the debate of whether different priors should be used for estimation and model selection, showing that selection priors may actually be desirable for high-dimensional estimation.

Keywords: Model Selection, MCMC, Non Local Priors, Bayesian Model.