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Nova · Professor Researcher · re-ranking top 20…

Robert Kohn

Verified

Brown University · Environmental Health Sciences

Active 1936–2026

h-index53
Citations13.9k
Papers53579 last 5y
Funding
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Research topics

  • Mathematics
  • Computer science
  • Statistics
  • Econometrics
  • Applied mathematics

Selected publications

  • Analysing symbolic data by pseudo-marginal methods

    Statistics and Computing · 2026-04-02

    articleOpen access

    Abstract Symbolic data analysis (SDA) aggregates large individual-level datasets into a small number of distributional summaries, such as random rectangles or random histograms. The inference is carried out using these summaries in place of the original dataset, resulting in computational gains at the loss of some information. In likelihood-based SDA, the likelihood function is characterised by an integral with a large exponent, which limits the method’s utility as for typical models the integral is unavailable in closed form. In addition, the likelihood function is known to produce biased parameter estimates in some circumstances. Our article develops a Bayesian framework for SDA methods in these settings that resolves the issues resulting from integral intractability and biased parameter estimation using pseudo-marginal Markov chain Monte Carlo methods. We develop an exact but computationally expensive method based on path sampling and the Poisson estimator, and a much faster, but approximate, method based on a Taylor expansion. Through simulation and real-data examples we demonstrate the performance of the developed methods, showing large reductions in computation time compared to the full-data analysis, with only a small loss of information.

  • A Beta Cauchy-Cauchy (BECCA) shrinkage prior for Bayesian variable selection

    arXiv (Cornell University) · 2025-01-13

    preprintOpen access

    This paper introduces a novel Bayesian approach for variable selection in high-dimensional and potentially sparse regression settings. Our method replaces the indicator variables in the traditional spike and slab prior with continuous, Beta-distributed random variables and places half Cauchy priors over the parameters of the Beta distribution, which significantly improves the predictive and inferential performance of the technique. Similar to shrinkage methods, our continuous parameterization of the spike and slab prior enables us explore the posterior distributions of interest using fast gradient-based methods, such as Hamiltonian Monte Carlo (HMC), while at the same time explicitly allowing for variable selection in a principled framework. We study the frequentist properties of our model via simulation and show that our technique outperforms the latest Bayesian variable selection methods in both linear and logistic regression. The efficacy, applicability and performance of our approach, are further underscored through its implementation on real datasets.

  • 27. INTERNATIONAL HUMAN RIGHTS IN THE ELDERLY

    American Journal of Geriatric Psychiatry · 2025-07-15

    article1st authorCorresponding
  • Calibrated Bayesian inference for random fields on large irregular domains using the debiased spatial Whittle likelihood

    ArXiv.org · 2025-05-29

    preprintOpen accessSenior author

    Bayesian inference for stationary random fields is computationally demanding. Whittle-type likelihoods in the frequency domain based on the fast Fourier Transform (FFT) have several appealing features: i) low computational complexity of only $\mathcal{O}(n \log n)$, where $n$ is the number of spatial locations, ii) robustness to assumptions of the data-generating process, iii) ability to handle missing data and irregularly spaced domains, and iv) flexibility in modelling the covariance function via the spectral density directly in the spectral domain. It is well known, however, that the Whittle likelihood suffers from bias and low efficiency for spatial data. The debiased Whittle likelihood is a recently proposed alternative with better frequentist properties. We propose a methodology for Bayesian inference for stationary random fields using the debiased spatial Whittle likelihood, with an adjustment from the composite likelihood literature. The adjustment is shown to give a well-calibrated Bayesian posterior as measured by coverage properties of credible sets, without sacrificing the quasi-linear computation time. We apply the method to simulated data and two real datasets.

  • Variational Bayesian inference for models with nuisance parameters and an intractable likelihood

    Statistics and Computing · 2025-06-17

    articleOpen accessSenior author

    Abstract A primary challenge in Bayesian analysis lies in computing the posterior distribution of model parameters, especially for models with a large number of parameters or intractable likelihoods. Often, the focus is on a subset of parameters, with the remainder regarded as nuisance parameters introduced for computational convenience. This complexity necessitates refined computational methods. Variational Bayesian inference (VB) has emerged as a powerful solution, enhancing computational efficiency by recasting inference as an optimization problem within a family of tractable distributions. However, common VB techniques sometimes fall short, especially for models with nuisance parameters or intractable likelihoods. After identifying characteristics of suboptimal VB methods, we build upon the Hybrid Variational Bayes (HVB) approach introduced by Loaiza-Maya et al. (2022) and develop an extended and unified HVB framework designed to achieve more precise Bayesian inference in such scenarios. Through theoretical exploration and a series of illustrative examples, our approach demonstrates notable improvements over traditional VB methods.

  • Bayesian inference for evidence accumulation models with regressors.

    Psychological Methods · 2025-02-13

    articleOpen access

    Evidence accumulation models (EAMs) are an important class of cognitive models used to analyze both response time and response choice data recorded from decision-making tasks. Developments in estimation procedures have helped EAMs become important both in basic scientific applications and solution-focused applied work. Hierarchical Bayesian estimation frameworks for the linear ballistic accumulator (LBA) model and the diffusion decision model (DDM) have been widely used, but still suffer from some key limitations, particularly for large sample sizes, for models with many parameters, and when linking decision-relevant covariates to model parameters. We extend upon previous work with methods for estimating the LBA and DDM in hierarchical Bayesian frameworks that include random effects that are correlated between people and include regression-model links between decision-relevant covariates and model parameters. Our methods work equally well in cases where the covariates are measured once per person (e.g., personality traits or psychological tests) or once per decision (e.g., neural or physiological data). We provide methods for exact Bayesian inference, using particle-based Markov chain Monte-Carlo, and also approximate methods based on variational Bayesian (VB) inference. The VB methods are sufficiently fast and efficient that they can address large-scale estimation problems, such as with very large data sets. We evaluate the performance of these methods in applications to data from three existing experiments. Detailed algorithmic implementations and code are freely available for all methods. (PsycInfo Database Record (c) 2025 APA, all rights reserved).

  • The Current State of International Human Rights of Older Persons

    American Journal of Geriatric Psychiatry · 2025-08-21

    reviewOpen access1st authorCorresponding
  • Fast Variational Boosting for Latent Variable Models

    ArXiv.org · 2025-02-27

    preprintOpen accessSenior author

    We consider the problem of estimating complex statistical latent variable models using variational Bayes methods. These methods are used when exact posterior inference is either infeasible or computationally expensive, and they approximate the posterior density with a family of tractable distributions. The parameters of the approximating distribution are estimated using optimisation methods. This article develops a flexible Gaussian mixture variational approximation, where we impose sparsity in the precision matrix of each Gaussian component to reflect the appropriate conditional independence structure in the model. By introducing sparsity in the precision matrix and parameterising it using the Cholesky factor, each Gaussian mixture component becomes parsimonious (with a reduced number of non-zero parameters), while still capturing the dependence in the posterior distribution. Fast estimation methods based on global and local variational boosting moves combined with natural gradients and variance reduction methods are developed. The local boosting moves adjust an existing mixture component, and optimisation is only carried out on a subset of the variational parameters of a new component. The subset is chosen to target improvement of the current approximation in aspects where it is poor. The local boosting moves are fast because only a small number of variational parameters need to be optimised. The efficacy of the approach is illustrated by using simulated and real datasets to estimate generalised linear mixed models and state space models.

  • Particle MCMC and the correlated particle hybrid sampler for state space models

    Journal of Econometrics · 2024-05-01 · 1 citations

    articleOpen accessSenior authorCorresponding
  • ProDAG: Projected Variational Inference for Directed Acyclic Graphs

    arXiv (Cornell University) · 2024-05-24

    preprintOpen accessSenior author

    Directed acyclic graph (DAG) learning is a central task in structure discovery and causal inference. Although the field has witnessed remarkable advances over the past few years, it remains statistically and computationally challenging to learn a single (point estimate) DAG from data, let alone provide uncertainty quantification. We address the difficult task of quantifying graph uncertainty by developing a Bayesian variational inference framework based on novel, provably valid distributions that have support directly on the space of sparse DAGs. These distributions, which we use to define our prior and variational posterior, are induced by a projection operation that maps an arbitrary continuous distribution onto the space of sparse weighted acyclic adjacency matrices. While this projection is combinatorial, it can be solved efficiently using recent continuous reformulations of acyclicity constraints. We empirically demonstrate that our method, ProDAG, can outperform state-of-the-art alternatives in both accuracy and uncertainty quantification.

Frequent coauthors

  • Minh‐Ngoc Tran

    University of Sydney

    115 shared
  • David Gunawan

    University of Wollongong

    97 shared
  • David J. Nott

    National University of Singapore

    82 shared
  • Mattias Villani

    77 shared
  • Craig F. Ansley

    68 shared
  • Matias Quiroz

    63 shared
  • Chris Carter

    ARC Centre of Excellence for Mathematical and Statistical Frontiers

    52 shared
  • Jerrold E. Marsden

    51 shared
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