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Title: On high-dimensional cross-validation and accumulated prediction error Authors:  Wei-Cheng Hsiao - Soochow University (Taiwan) [presenting]
Ching-Kang Ing - National Tsing Hua University (Taiwan)
Wei-Ying Wu - National Dong Hwa University (Taiwan)
Abstract: Cross validation (CV) has been one of the most popular methods for model selection. By splitting $n$ data points into a training sample of size $nc$ and a validation sample of size $nv$ in which $nv/n$ approaches 1 and $nc$ tends to infinity, it has been shown that subset selection based on CV is consistent in a regression model of $p$ candidate variables with $p << n$. However, in the case of $p >> n$, not only does CV's consistency remain undeveloped, but subset selection is also practically infeasible. Instead of subset selection, we suggest using CV as a backward elimination tool for excluding redundant variables that enter regression models through high-dimensional variable screening methods such as LASSO, LARS, ISIS, and OGA. By choosing a $nv$ such that $nv/n$ converges to 1 at a rate faster than the one suggested previously, we establish the selection consistency of the proposed method. Accumulated prediction error (APE), on the other hand, can be viewed as a counterpart of CV in situations where a random split of data is pointless (e.g., when data are serially correlated). While APE's behavior in the case of $p << n$ has been well understood, no results have been reported regarding its performance in the high-dimensional case. To fill this gap, we provide a high-dimensional amendment of APE and justify its asymptotic validity. Simulation evidence will also be presented.