So these managers eschew the passive approach to tracking an index in favor of a semi-active approach to portfolio management.

FORBES: Enhanced Index Funds: Can They Deliver Low-Risk Returns?

An index tracking prices that companies pay for goods jumped up sharply in July, which means inflation is a growing threat.

NPR: Inflation A Growing Threat As Producer Prices Jump

With three of the country's banks now nationalized and their market caps reduced to zero, the OMXI15, an index tracking Iceland's 15 biggest shares, had to be recalculated, so some traders were confronted with a startling 76.0% drop in leading shares.

FORBES: Market Scan

The suppliers of bond ETFs get around the liquidity problem by using representative sampling, which simply means tracking only a sufficient number of bonds to represent an index.

FORBES: An Easy Way To Add Fixed-Income To Your Portfolio

The expectation that an index fund will get EXACTLY the return of the target index sets the stage for an interesting problem: Zero tracking error is achievable, but it comes at a very high price.

FORBES: Getting Over Index Investing With A Better Way

If you must buy an index fund, we said, go for a broader fund tracking the Wilshire 5000.

FORBES: Follow Through

U.S. mutual funds that invested in large growth stocks in 2012 returned an average of 15.3%, while the similar ETFs tracking the index returned 16.4%, according to Morningstar.

WSJ: Investors Sour on Pro Stock Pickers

The index tracking leveraged-loan trading fell 6% over the last three months, an indication that the weakening credits will force banks to write-off a chunk of their exposures.

FORBES: Banking's Black Hole

These two scenarios can create an environment where performance expectations of investors may not be met due to the tracking error versus the underlying commodity index that is created.

FORBES: Three Ways To Gain Exposure To Oil