For instance, providers can’t expect to come up with another profitable S&P 500 index-based ETF as the iShares Core S&P 500 Index ETF (NYSEArca: IVV), SPDR S&P 500 ETF (NYSEArca; SPY) and Vanguard S&P 500 ETF (NYSEArca: VOO) account for a combined $185.5 billion in assets. [Fundamental ETFs Try to Challenge DFA: Report]

Consequently, fund sponsors engineered modified strategies, or “enhanced” indexices, that expand on the traditional benchmark, including the Guggenheim S&P 500 Equal Weight ETF (NYSEArca: RSP), iShares S&P 500 Growth Index ETF (NYSEArca: IVW), iShares S&P 500 Value Index ETF (NYSEArca: IVE) and PowerShares S&P 500 Low Volatility ETF (NYSEArca: SPLV). [Alternative Weighted Index ETFs Attract Heavy Inflows: Schwab]

For more information on ETF indexing, visit our indexing category.

Max Chen contributed to this article.

Full disclosure: Tom Lydon’s clients own SPY.