## The Annals of Statistics

### Deviation optimal learning using greedy $Q$-aggregation

#### Abstract

Given a finite family of functions, the goal of model selection aggregation is to construct a procedure that mimics the function from this family that is the closest to an unknown regression function. More precisely, we consider a general regression model with fixed design and measure the distance between functions by the mean squared error at the design points. While procedures based on exponential weights are known to solve the problem of model selection aggregation in expectation, they are, surprisingly, sub-optimal in deviation. We propose a new formulation called $Q$-aggregation that addresses this limitation; namely, its solution leads to sharp oracle inequalities that are optimal in a minimax sense. Moreover, based on the new formulation, we design greedy $Q$-aggregation procedures that produce sparse aggregation models achieving the optimal rate. The convergence and performance of these greedy procedures are illustrated and compared with other standard methods on simulated examples.

#### Article information

Source
Ann. Statist., Volume 40, Number 3 (2012), 1878-1905.

Dates
First available in Project Euclid: 16 October 2012

Permanent link to this document
https://projecteuclid.org/euclid.aos/1350394520

Digital Object Identifier
doi:10.1214/12-AOS1025

Mathematical Reviews number (MathSciNet)
MR3015047

Zentralblatt MATH identifier
1257.62037

#### Citation

Dai, Dong; Rigollet, Philippe; Zhang, Tong. Deviation optimal learning using greedy $Q$-aggregation. Ann. Statist. 40 (2012), no. 3, 1878--1905. doi:10.1214/12-AOS1025. https://projecteuclid.org/euclid.aos/1350394520

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