Penalized model-based clustering with cluster-specific diagonal covariance matrices and grouped variables

TL;DR

This paper introduces a novel penalized model-based clustering method that allows for cluster-specific diagonal covariance matrices and grouped variable selection, improving clustering accuracy in high-dimensional, noisy data such as microarrays.

Contribution

It extends existing penalized likelihood clustering methods by incorporating cluster-specific covariance matrices and group variable selection, enhancing flexibility and practical applicability.

Findings

Effective in high-dimensional microarray data analysis

Improves variable selection accuracy with grouped penalties

Demonstrates advantages through leukemia subtype discovery

Abstract

Clustering analysis is one of the most widely used statistical tools in many emerging areas such as microarray data analysis. For microarray and other high-dimensional data, the presence of many noise variables may mask underlying clustering structures. Hence removing noise variables via variable selection is necessary. For simultaneous variable selection and parameter estimation, existing penalized likelihood approaches in model-based clustering analysis all assume a common diagonal covariance matrix across clusters, which however may not hold in practice. To analyze high-dimensional data, particularly those with relatively low sample sizes, this article introduces a novel approach that shrinks the variances together with means, in a more general situation with cluster-specific (diagonal) covariance matrices. Furthermore, selection of grouped variables via inclusion or exclusion of a group of variables altogether is permitted by a specific form of penalty, which facilitates incorporating subject-matter knowledge, such as gene functions in clustering microarray samples for disease subtype discovery. For implementation, EM algorithms are derived for parameter estimation, in which the M-steps clearly demonstrate the effects of shrinkage and thresholding. Numerical examples, including an application to acute leukemia subtype discovery with microarray gene expression data, are provided to demonstrate the utility and advantage of the proposed method.