Physical-structure priors such as conservation laws, Hamiltonian forms, and symmetries can improve scientific machine learning when correct, but can degrade predictions when misspecified. Existing methods usually enforce a chosen structure or tune a soft penalty, without a calibrated rule for deciding whether to impose a prior, how strongly to impose it, which prior to use, or which subset of candidate laws holds. We introduce SPADE, Structure-Prior Adaptive Decision Estimation, a closed-form framework that treats this problem as shrinkage of the structure-violating block of an unconstrained estimator. SPADE uses one exact specification test and one estimand: the test decides whether the prior is supported by data, Stein-unbiased James-Stein shrinkage sets the enforcement strength with an $O(σ^2/n)$ oracle guarantee, and a gate commits to the hard prior only when the test certifies it. The same test yields consistent nested structure selection and Benjamini-Hochberg control for subset discovery in non-nested constraint families. Across a linear-subspace prior, a reservoir conservation law, and a nonlinear Hamiltonian prior on Duffing dynamics, SPADE tracks the oracle, beats a neural-network baseline, reduces correct-prior regret from $10.3\%$ to $2.6\%$, matches cross-validation with $1/71$ of the solves, selects the correct structure with $100\%$ accuracy, and recovers partial laws with controlled false relaxation.
Small area estimation borrows strength across domains to repair the poor precision of direct survey estimators. Two philosophies dominate the area-level literature. The first, descending from Ghosh and Rao (1994), borrows strength through structured Gaussian smoothing: an intrinsic conditional autoregression or its BYM2 reparameterization pools each area towards its neighbours. The second borrows strength globally but acts locally through a heavy-tailed global-local prior on area effects, of which the horseshoe of Carvalho et al. (2010) is the canonical instance; Tang et al. (2018) first brought this idea to small area estimation. We study the horseshoe Fay-Herriot model with known unequal sampling variances and make four contributions. First, a tail-robustness theorem: through a heteroscedastic Tweedie identity the posterior mean leaves strongly signalled areas essentially unshrunk, bounding the influence of an outlying direct estimate, unlike Gaussian random-effect models. Second, standardizing by the known design variances transfers the minimax contraction and credible-set theory of the homoscedastic sequence model to the heteroscedastic Fay-Herriot problem; the posterior contracts at the nearly-black minimax rate, with a matching lower bound. Third, we give an account of when structured smoothing and global-local shrinkage each win. Fourth, an O(m) Gibbs sampler, simulations, and an analysis of the Scottish lip cancer data confirm the account: on strongly spatial data the smoother predicts held-out districts best, yet the horseshoe flags exceptional districts that smoothing suppresses. Throughout we argue, following the regular-variation theory of Bhadra et al. (2016), that these properties make the horseshoe a sound default prior for area effects: it borrows strength aggressively yet lets genuinely exceptional areas speak for themselves, with no tuning and no neighbourhood graph.
Mathieu Chalvidal, Florentin Coeurdoux, Eric Vanden-Eijndencs.LG stat.ML
We recast classical shrinkage of high-dimensional covariance estimators as empirical risk minimization over a parametric stochastic interpolant between a source and a target distribution. This formalism recovers known shrinkage estimators as special cases and reveals three distinct mechanisms for reducing statistical risk: (i) Scheduling: the interpolant schedule determines the class of admissible covariances, and hence the achievable risk. (ii) Flow maps and couplings: whereas naive constructions amount to assuming independence between the distributions, specific coupling structures (e.g., solutions of optimal transport problems) can lower the empirical risk. Moreover, non-linear flow maps realizing such couplings free the interpolant covariance from the eigenbasis of the empirical estimate, enabling eigenvector regularization. (iii) Early stopping: estimators defined by integrating a regressed vector field afford an additional bias-variance trade-off through approximation of the true interpolant distribution. We then propose a neural estimator of the interpolant, together with an upper bound on its quadratic risk in terms of the interpolant approximation error, and validate both on synthetic experiments. Finally, we apply the estimator to real neuroimaging data, demonstrating the additional regularization power this approach offers in practice.