Before revision:  Indeed, many existing plug-in approaches for the estimation of risk suffer from an unnecessary bias which leads to the underestimation of risk and negatively impacts backtesting results, especially in the small sample environment .
After revision:  Indeed, many existing plug-in approaches for the estimation of risk suffer from an unnecessary bias . This often leads to the underestimation of risk and negatively impacts backtesting results, especially in the small sample environment .