## Estimation of functionals of sparse covariance matrices.(English)Zbl 1327.62338

Summary: High-dimensional statistical tests often ignore correlations to gain simplicity and stability leading to null distributions that depend on functionals of correlation matrices such as their Frobenius norm and other $$\ell_{r}$$ norms. Motivated by the computation of critical values of such tests, we investigate the difficulty of estimation the functionals of sparse correlation matrices. Specifically, we show that simple plug-in procedures based on thresholded estimators of correlation matrices are sparsity-adaptive and minimax optimal over a large class of correlation matrices. Akin to previous results on functional estimation, the minimax rates exhibit an elbow phenomenon. Our results are further illustrated in simulated data as well as an empirical study of data arising in financial econometrics.

### MSC:

 62H12 Estimation in multivariate analysis 62H15 Hypothesis testing in multivariate analysis 62C20 Minimax procedures in statistical decision theory 62H25 Factor analysis and principal components; correspondence analysis
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