作者：George J. Jiang (Washington State University), Gulnara R. Zaynutdinova, Ph.D. (West Virginia University, Department of Finance), 张华丞（西南财经大学金融研究院）
We argue that mutual fund managers should trade actively only when the market presents opportunities to pick stocks with positive alpha. In this paper, we propose stock-selection opportunity measures and show that a significant portion of mutual funds time their active trading, i.e., they trade more when the market presents more stock-selection opportunities. We show that positive timers outperform negative timers by about 82 bps in annualized four-factor alpha over the subsequent six-month horizon and, more importantly, that stock-selection timing contributes significantly to fund performance even after controlling for fund managers’ stock-picking ability. Finally, we present evidence that on average funds with very high portfolio turnover are actually poor timers, whereas younger funds and funds with larger family size exhibit better skills in timing stock-selection.