papers

Papers

Preprints and articles by Øystein Sørensen.

Below is a list of my main methodological papers. For a complete publication list, se my Google Scholar Profile.

Mar 2026

A Hybrid NUTS-Gibbs Sampler with State Space Marginalization for Estimation of Dynamic Structural Equation Models with Binomial Outcomes

This paper presents a hybrid NUTS-Gibbs sampler for dynamic structural equation models with binomial outcomes. The Gibbs step handles Pólya-Gamma latent variables from a logit link, while the NUTS step uses a Kalman filter to marginalize over latent states. arXiv preprint.

  • DSEM
  • intensive longitudinal data
  • NUTS
  • Gibbs sampler
  • Pólya-Gamma
  • binomial
  • Kalman filter
Mar 2026

A Semiparametric Nonlinear Mixed Effects Model with Penalized Splines Using Automatic Differentiation

We present an estimation procedure for nonlinear mixed-effects models in which the population trajectory is represented by penalized splines and adapted to individuals via subject-specific transformation parameters. Exact derivatives are obtained via automatic differentiation implemented through Template Model Builder. arXiv preprint.

  • nonlinear mixed effects
  • penalized splines
  • automatic differentiation
  • Template Model Builder
  • Laplace approximation
  • growth curves
Oct 2025

Gaining Brain Insights by Tapping into the Black Box: Linking Structural MRI Features to Age and Cognition using Shapley-Based Interpretation Methods

This paper evaluates multiple interpretability techniques for machine learning models applied to neuroimaging data, including SHAP and SAGE. We trained XGBoost models to predict age and fluid intelligence using UK Biobank data and found that subcortical mean intensities are associated with brain aging, while fluid intelligence prediction is driven by the hippocampus and cerebellum. Published in Neuroinformatics.

  • explainable AI
  • SHAP
  • neuroimaging
  • brain aging
  • machine learning
  • XGBoost
Jan 2025

Modeling Cycles, Trends and Time-Varying Effects in Dynamic Structural Equation Models with Regression Splines

This paper considers rank and preference modeling for the case in which data arrive sequentially, rather than in a batch. The goal is to compute the posterior distribution incrementally in time, so that it can be quickly updated when new data arrives. To this end, we develop a sequential Monte Carlo algorithm for the Bayesian Mallows model. arXiv preprint currently under revision.

  • DSEM
  • intensive longitudinal data
  • regression splines
  • smoothing
  • Stan
Dec 2024

Sequential Rank and Preference Learning with the Bayesian Mallows Model

This paper considers rank and preference modeling for the case in which data arrive sequentially, rather than in a batch. The goal is to compute the posterior distribution incrementally in time, so that it can be quickly updated when new data arrives. To this end, we develop a sequential Monte Carlo algorithm for the Bayesian Mallows model. Published in Bayesian Analysis.

  • Mallows mixtures
  • partial rankings
  • particle filter
  • preference learning
  • SMC$^{2}$
Jun 2023

Longitudinal Modeling of Age-Dependent Latent Traits with Generalized Additive Latent and Mixed Models

This paper was motivated by the need to use flexible spline models to model how cognitive abilities change with age, and investigating how changes in abilities in certain cognitive domains can be explained by changes in the brain. To this end we developed a framework called Generalized Additive Latent and Mixed Models (GALAMM), combining generalized additive mixed models, structural equation modeling, and mxied effect modeling. We also propose algorithms for estimating the models, using sparse matrix methods and automatic differentation. Published in Psychometrika.

  • generalized additive mixed models
  • latent variable modeling
  • lifespan trajectories
  • mixed response
Feb 2021

A recipe for accurate estimation of lifespan brain trajectories, distinguishing longitudinal and cohort effects

This paper considers estimation of lifespan brain trajectories from longitudinal data, using generalized additive mixed models. It studies how to distinguish longitudinal effects from cohort effects, and shows example code in R which practitioners can use for their own data. Published in NeuroImage.

  • generalized additive models
  • longitudinal data analysis
  • cohort effects
  • MRI
Jan 2021

Meta-analysis of generalized additive models in neuroimaging studies

This paper considers meta analysis of nonlinear functions estimated by generalized additive (mixed) models.

  • generalized additive models
  • meta analysis
  • MRI