# Statistics Colloquium Series

## Date:

Monday, April 25, 2022, 12:00pm to 1:00pm

## Location:

Science Center, Room 316

Our upcoming event for the Statistics Department Colloquium Series is scheduled for this Monday, April 25th from 12:00 – 1:00pm (ET) and will be an in person presentation in room 316 of the Science Center. The speaker is Yury Polyanskiy who is an Associate Professor in the Department of Electrial Engineering and Computer Sciences at Massachusetts Institute of Technology.

Title: Empirical Bayes estimators for Poisson and normal means

Abstract : We consider the classical problems of estimating the mean of an n-dimensional normally (with identity covariance matrix) or Poisson distributed vector under the squared loss. The framework of empirical Bayes (EB), put forth by Robbins'1956, combines Bayesian and frequentist mindsets by postulating that the mean's coordinates are sampled iid from an unknown prior and aims to use a fully data-driven estimator to compete with the Bayesian oracle that knows the true prior. The central figure of merit is the regret, namely, the total excess risk over the Bayes risk in the worst case (over the class of, e.g., priors with a given support). Although this paradigm was introduced more than 60 years ago, little was known about the asymptotic scaling of the optimal regret before our work established it to be $\Theta((\log n/\log \log n)^2)$ for the Poisson case. The same rate is shown to be a lower bound for the normal case, verifying and strengthening upon an old conjecture of $\omega(1)$ due to Singh'1979.
We will also discuss practical implementation of EB estimators. The most performant of those are obtained by first running a non-parametric maximum likelihood (NPMLE) to estimate the unknown prior, and then computing (via Bayes) the posterior mean with respect to the estimated prior. We will discuss empirical results on sports data and short-term time series forecasting.

Based on joint works with Yihong Wu, Soham Jana and Anzo Teh.