The Annals of Statistics

Optimal classification in sparse Gaussian graphic model

Yingying Fan, Jiashun Jin, and Zhigang Yao

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Abstract

Consider a two-class classification problem where the number of features is much larger than the sample size. The features are masked by Gaussian noise with mean zero and covariance matrix $\Sigma$, where the precision matrix $\Omega=\Sigma^{-1}$ is unknown but is presumably sparse. The useful features, also unknown, are sparse and each contributes weakly (i.e., rare and weak) to the classification decision.

By obtaining a reasonably good estimate of $\Omega$, we formulate the setting as a linear regression model. We propose a two-stage classification method where we first select features by the method of Innovated Thresholding (IT), and then use the retained features and Fisher’s LDA for classification. In this approach, a crucial problem is how to set the threshold of IT. We approach this problem by adapting the recent innovation of Higher Criticism Thresholding (HCT).

We find that when useful features are rare and weak, the limiting behavior of HCT is essentially just as good as the limiting behavior of ideal threshold, the threshold one would choose if the underlying distribution of the signals is known (if only). Somewhat surprisingly, when $\Omega$ is sufficiently sparse, its off-diagonal coordinates usually do not have a major influence over the classification decision.

Compared to recent work in the case where $\Omega$ is the identity matrix [Proc. Natl. Acad. Sci. USA 105 (2008) 14790–14795; Philos. Trans. R. Soc. Lond. Ser. A Math. Phys. Eng. Sci. 367 (2009) 4449–4470], the current setting is much more general, which needs a new approach and much more sophisticated analysis. One key component of the analysis is the intimate relationship between HCT and Fisher’s separation. Another key component is the tight large-deviation bounds for empirical processes for data with unconventional correlation structures, where graph theory on vertex coloring plays an important role.

Article information

Source
Ann. Statist., Volume 41, Number 5 (2013), 2537-2571.

Dates
First available in Project Euclid: 19 November 2013

Permanent link to this document
https://projecteuclid.org/euclid.aos/1384871345

Digital Object Identifier
doi:10.1214/13-AOS1163

Mathematical Reviews number (MathSciNet)
MR3161437

Zentralblatt MATH identifier
1294.62061

Subjects
Primary: 62G05: Estimation
Secondary: 62G32: Statistics of extreme values; tail inference

Keywords
Chromatic number Fisher’s LDA Fisher’s separation phase diagram precision matrix rare and weak model sparse graph

Citation

Fan, Yingying; Jin, Jiashun; Yao, Zhigang. Optimal classification in sparse Gaussian graphic model. Ann. Statist. 41 (2013), no. 5, 2537--2571. doi:10.1214/13-AOS1163. https://projecteuclid.org/euclid.aos/1384871345


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