Strategies selected by combining multiple signals suffer severe overfitting biases, because underlying signals are typically signed such that each predicts positive in-sample returns. "Highly significant" backtested performance is easy to generate by selecting stocks on the basis of combinations...

High volatility and high beta stocks tilt strongly to small, unprofitable, and growth firms. These tilts explain the poor absolute performance of the most aggressive stocks. In conjunction with the well documented inability of the Fama and French three-factor model to price small growth stocks,...

Strategies selected by combining multiple signals suffer severe overfitting biases, because underlying signals are typically signed such that each predicts positive in-sample returns. “Highly significant” backtested performance is easy to generate by selecting stocks on the basis of...