The only type of general equity fund that the sector portfolios did not beat was the group that tracks the Standard & Poor's 500-stock index.

But he is not obliged to guarantee that a trust tracks its index on a wild day.

There are plenty of reasons to own a fund that tracks the Standard & Poor's 500-stock index, and they may have seemed particularly compelling in recent years.

But many economists also track the Federal Reserve Board's index of the dollar's value against 10 other trade-weighted currencies.

Investors who buy a fund that tracks the Standard & Poor's 500-stock index may expect the fund's return to approximate the index's.

Investors' appetite for funds that track the Standard & Poor's 500-stock index seems insatiable, and more fund companies are chasing those dollars.

In effect, the arbitragers force an exchange-traded fund to track its index.

Near the high end, a fund that tracks the Standard & Poor's 500-stock index had an average return of 12 percent a year.

Spiders track the Standard & Poor's 500-stock index, making them a popular way to bet for or against the market.

The expense ratios on funds that track the Standard & Poor's 500-stock index generally range from 0.18 to 0.40.