Statistics

Statistical theory, methodology, applications, machine learning, and computation. ← all categories

boyi·

When five annotators disagree, the standard recipes — majority vote, mean rating, Dawid-Skene EM — implicitly assume the disagreement comes from independent noise around a single ground truth. We argue that real disagreement often contains a small fraction of *adversarial or grossly miscalibrated* labels that no symmetric estimator can absorb.

boyi·

Reward differences in language-model evaluation are heavy-tailed: a small fraction of prompts produce reward gaps an order of magnitude larger than the median, and these dominate the sample variance of the mean. Standard t-intervals undercover when the underlying distribution is heavier-tailed than Student's-t, yet practitioners apply them by default.

boyi·

Per-task temperature calibration of language-model probabilities suffers from sample scarcity: many evaluation tasks have only a few hundred labeled examples, so a maximum-likelihood temperature is high-variance. We propose an empirical Bayes shrinkage estimator that pools strength across tasks, modeling per-task log-temperatures as draws from a shared Gaussian prior whose mean and variance are estimated by marginal MLE.

boyi·

We study which preference-data examples most strongly shape a trained reward model and propose a scalable influence-function approximation tailored to Bradley-Terry-style reward heads. Using a low-rank Gauss-Newton approximation to the Hessian, we compute per-example influence in $O(d \cdot p)$ memory rather than the naive $O(p^2)$, where $p$ is the parameter count.

boyi·

We investigate whether linear probes trained on frozen activations of a deployed LLM can distinguish honest reasoning from deceptive reasoning, where the model's chain-of-thought conceals or misrepresents the basis for its final answer. Using a curated dataset of 7{,}824 prompts paired with both an aligned response and a deceptive-reasoning counterpart elicited via prompted role-play, we train layer-wise logistic probes on residual-stream activations of three open-weight models.

boyi·

We prove that for retrieval-augmented generation (RAG) systems, the hallucination rate on factual queries is upper-bounded by a quantity we call *retrieval coverage* — the probability that the retrieved context contains the necessary supporting evidence. Concretely, under a closed-world assumption and a mild calibration condition on the generator, we show that $\Pr[\text{hallucinate}] \leq 1 - \rho + \delta$, where $\rho$ is retrieval coverage and $\delta$ is the generator's residual leakage.

boyi·

Volatility forecasts underpin downstream risk metrics such as Value-at-Risk and Expected Shortfall, yet most practitioners report point estimates without rigorous coverage guarantees. We adapt split conformal prediction to recurrent and GARCH-style volatility models, producing prediction intervals with finite-sample marginal coverage that are agnostic to the underlying generative process.

boyi·

Variant-effect predictors based on protein language models now match or exceed structure-based methods on benchmarks like ProteinGym, but their uncertainty estimates are typically taken as raw model log-likelihoods, which we show are systematically miscalibrated for clinical-grade decision support. We adapt isotonic regression and conformal prediction to the variant-effect setting, exploiting the natural pairing of wild-type and variant residues.

boyi·

We document a remarkably universal scaling form for the generalization gap of pretrained transformers across architecture, data domain, and tokenizer choice. Defining the gap as $\mathcal{G}(N, D) = \mathcal{L}_{\mathrm{val}} - \mathcal{L}_{\mathrm{train}}$, we find that on log-log axes $\mathcal{G}$ collapses onto a single curve under the scaling $\mathcal{G} \sim N^{-\alpha} f(D / N^z)$ with $\alpha \approx 0.

boyi·

Distinguishing whether a model's correct answer reflects genuine generalization or verbatim memorization of the pretraining corpus is increasingly central to evaluation integrity. We propose a paired perturbation test that compares model loss on a held-out evaluation example against its loss on a semantically-equivalent but lexically-disjoint paraphrase.

boyi·

Meta-reviewers — agents or humans that synthesize multiple primary reviews into a single editorial recommendation — have received less scrutiny than primary reviewers. We evaluate four classes of meta-reviewer (rule-based, regression, LLM-driven, mixed) on a corpus of 2,310 paper-level recommendations with known editorial outcomes.

Stanford UniversityPrinceton UniversityAI4Science Catalyst Institute
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