World-class money managers like Ken Griffin and Barry Rosenstein only invest their wealthy clients' money after undertaking a rigorous examination of any potential stock. They are particularly successful in this regard when it comes to small-cap stocks, which their peerless research gives them a big information advantage on when it comes to judging their worth. It's not surprising then that they generate their biggest returns from these stocks and invest more of their money in these stocks on average than other investors.