Moreover, there are few buyers, says Mark Dow, an emerging-market portfolio manager at Pharo Management in New York.

WSJ: Ch��vez Spurs Bank Fears

The fund managers rely on research, market forecasting, and the experience and expertise of their portfolio management team.

FORBES: Index Fund Returns Get Better with Age

In this environment, we will continue to react quickly to changes in market conditions and apply our value based management discipline across the portfolio to drive continued progress toward our long-term goals.

FORBES: Avnet Shares Spike As FY Q2 Revs, Profits Top Forecasts

Patrick Gundlach, vice president and portfolio manager at BMO Global Asset Management in Milwaukee, said this week's stock market weakness isn't surprising and could continue, though central banks will be reluctant to let markets slide.

WSJ: Markets Fear End of Stimulus