Let's say there are 10 stocks in the same industry/sector. One stock is down 4% or so while the other 9 stocks are up 5%. Would you buy the stock that is down hoping that it would fall in line with the other stocks in its industry/sector or short it because it's an underperformer? Assume there is no news. Also the same question for vise versa where one stock up, 9 stocks down.