Momentum investing traditionally implies long-only strategies. I'm trying to adapt its ideas for shorting stocks when the market trend is bearish. For choosing stocks, is it better to use their absolute returns (volatility adjusted) or performance relative to some index? Even more important question. What time period to use? 12 months or 6 months or some other? I understand that one can answer all these questions with the help of backtesting. But I'm still a newbie. Conducting such a backtesting would be an overkill for me.