Polynomial Log-Marginals and Tweedie's Formula : When Is Bayes Possible?
多项式对数边际密度与 Tweedie 公式:何时存在贝叶斯解释?
Motivated by Tweedie's formula for the Compound Decision problem, we examine the theoretical foundations of empirical Bayes estimators that directly model the marginal density $m(y)$. Our main result shows that polynomial log-marginals of degree $k \ge 3 $ cannot arise from any valid prior distribution in exponential family models, while quadratic forms correspond exactly to Gaussian priors. This provides theoretical justification for why certain empirical Bayes decision…