The Cluster Graphical Lasso for improved estimation of Gaussian graphical models

TL;DR

This paper introduces the cluster graphical lasso, a novel method that improves Gaussian graphical model estimation by replacing single linkage clustering with alternative clustering techniques, leading to better performance in high-dimensional data analysis.

Contribution

The paper proposes the cluster graphical lasso, which enhances the graphical lasso by using alternative clustering methods for better connected component detection and model estimation.

Findings

Model selection consistency established for the method.

Improved performance over traditional graphical lasso in simulations.

Effective application demonstrated on diverse real-world datasets.

Abstract

We consider the task of estimating a Gaussian graphical model in the high-dimensional setting. The graphical lasso, which involves maximizing the Gaussian log likelihood subject to an l1 penalty, is a well-studied approach for this task. We begin by introducing a surprising connection between the graphical lasso and hierarchical clustering: the graphical lasso in effect performs a two-step procedure, in which (1) single linkage hierarchical clustering is performed on the variables in order to identify connected components, and then (2) an l1-penalized log likelihood is maximized on the subset of variables within each connected component. In other words, the graphical lasso determines the connected components of the estimated network via single linkage clustering. Unfortunately, single linkage clustering is known to perform poorly in certain settings. Therefore, we propose the cluster graphical lasso, which involves clustering the features using an alternative to single linkage clustering, and then performing the graphical lasso on the subset of variables within each cluster. We establish model selection consistency for this technique, and demonstrate its improved performance relative to the graphical lasso in a simulation study, as well as in applications to an equities data set, a university webpage data set, and a gene expression data set.