Bayesian Factorised Granger-Causal Graphs For Multivariate Time-series Data

Introduction

The interpretation and understanding of causal relationships in multivariate time-series (MTS) data are crucial across a range of fields from neuroscience to economics. Fundamentally, Granger causality provides a valuable framework for discovering causal relations, quantifying the ability to predict the future value of one series using past values of another. Traditional Vector autoregressive (VAR) models and their Bayesian counterparts are commonly adopted for such analysis, with recent advancements integrating deep learning techniques. However, these methods often require large amounts of data, are sensitive to hyperparameter settings, and may lack in providing uncertainty quantification for decision-making tasks - a gap this research aims to bridge.

Bayesian VAR for Granger Causality

The proposed Bayesian VAR model with a hierarchical graph prior introduces a new approach to discovering binary Granger causal relations by distinctly modelling the underlying causal structure of MTS data. By decoupling binary causal relations from the VAR coefficients, this Bayesian framework allows direct sampling of potential causal graphs, providing a principled measure of uncertainty in causal inference.

Unlike existing models that incorporate sparsity through penalized coefficients or after-the-fact thresholding, our model employs a sparsity-inducing mechanism intrinsic to its Bayesian hierarchical structure. Through this mechanism, our method adapts to the sparsity level of the given MTS dataset efficiently.

Inferential Strengths and Performance

The hierarchical graph prior introduced in this model offers several advantages:

• It promotes robust uncertainty quantification by modelling the posterior over Granger causal graphs.
• It contains a flexible sparsity control mechanism suitable for sparse datasets.
• It reduces reliance on hyperparameter tuning, which is particularly beneficial where no ground-truth graph is available for validation.

Comprehensively tested on benchmark datasets, the proposed method achieves remarkable performance against both contemporary Bayesian VAR methods and more recent deep learning-based VAR models. This performance advantage is especially pronounced with sparse time-series data.

Efficient Inference Algorithm

Crucially, the efficiency of the algorithm stems from the close-form posteriors available for all variables in the model, allowing effective Gibbs sampling-based inference. This aspect makes the method particularly practical for applied purposes, as it offers stable convergence with quicker computations.

Conclusion

The paper presents a Bayesian VAR method that adeptly addresses existing challenges in Granger causal discovery from MTS data. By providing reliable uncertainty quantification and requiring fewer hyperparameters, it sets a benchmark for sparse MTS datasets. While it assumes linear dynamics and may not immediately apply to more intricate datasets, the Poisson Factorised Granger-Causal Graph (PFGCG) model stands as a potent tool in the domain of causal analysis. The implications of this research are profound, given the foundational nature of causal reasoning in scientific enquiry and the growing interest in robust, interpretable methods in machine learning.

The introduction of PFGCG model in the causal inference landscape marks a progressive shift towards techniques that accommodate data sparsity and provide clear uncertainty measures, addressing key concerns in critical decision-making scenarios.