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LONG BEACH, Calif. (MarketWatch) — Everyone wants something for nothing, and the desire can only grow at times like this when it seems as if just about every investment is returning not much of anything.

That could explain the rising trading volume in two exchange-traded funds that track stock indexes, such as the Standard & Poor’s 500 SPX, +1.26%  , but that hold the constituent stocks in systematically altered proportions.

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The ETFs, Guggenheim S&P 500 Equal Weight RSP, +1.28%   and PowerShares FTSE RAFI U.S. 1000 Portfolio PRF, +1.23%  , belong to a class of funds that professionals call “smart-beta,” a name that suggests a belief that the funds provide broad-market exposure with a bit of beneficial tweaking. (Beta is the term used for the component of an asset’s performance that can be accounted for by market movements as opposed to, say, a fund manager’s skill.)

Smart-beta funds deviate from conventional index allocations according to standard formulas that reflect theories about the underlying drivers of relative performance within an index. The ideas behind the Guggenheim and RAFI funds are similar:

Indexes like the S&P 500 are capitalization-weighted, meaning that investors have bigger stakes in companies with higher market values. The biggest components of such indexes are either the largest companies, which logic and arithmetic suggest would have limited growth prospects, or else they just seem bigger because their stocks are overvalued.

Either way, the thinking goes, those companies are likely to underperform and so a fund that holds them in lower proportions than the index should do better than a straight index fund. It’s a sensible notion, and it dovetails with long records of outperformance by value stocks over growth stocks and by smaller companies over larger ones.

You know what? It actually works.

Since the beginning of 2006, when PowerShares FTSE RAFI U.S. 1000 began trading (the Guggenheim fund has been around since 2003), the two funds have produced almost identical total cumulative returns, 62% and 60%, respectively, through June. More important, they have raced ahead of SPDR S&P 500 SPY, +1.27%   the index fund that plays it straight in tracking the S&P 500; it returned a mere 33%.

The superior results have been there from just after the market’s blastoff in 2009. They accelerated last fall, probably because of the conspicuously poor performance of Apple AAPL, +1.81%  , which had been the largest stock in the S&P 500 by far until Exxon Mobil XOM, +0.24%  took the lead as Apple’s share price tumbled. Because of how the portfolios are put together, Apple would have a smaller weighting in the smart-beta funds that it does in the cap-weighted S&P 500.

Are there drawbacks to these smart-beta ETFs? Nothing obvious. Both have annual expenses of 0.40%, compared to 0.10% for the conventional S&P 500 ETF, which is larger than the other two and has less-periodic portfolio rebalancing. But the higher expenses have not prevented the smart-beta funds from beating their more mainstream rival.

The smart-beta funds do trade with slightly more volatility, no doubt a reflection of their smaller-company bias. Even so, their Sharpe ratios, which measure risk-adjusted performance, are quite a bit higher, meaning better.

These portfolios are not immune to bear markets; they got pounded in 2008-09 like other stock funds. But they did no worse than the broad market, and have done a fair bit better during the good times since then. A combination like that is as close as fund investors are likely to get to having something for nothing.