NEW YORK (MarketWatch) — Most indexed investors have at least one broad-based fund in their portfolios, but relatively few choose the broadest of all — a fund based on a global index.

Fiddling with allocations to a U.S. fund, an ex-U.S. developed markets fund and an emerging markets fund is fine if there is a purpose to it. If not, you might consider an exchange-traded fund based on a global index, which wraps the world’s equity-market pieces into a single package.

ETF Database lists 154 global ETFs, but most of them focus on sectors and even thinner slices, such as “junior gold miners” and “cloud computing.” In this article, we will look at four broad-perspective global funds that could be suitable for worldwide equity exposure. The funds are:

Name Symbol No. of Stocks Net Assets iShares MSCI ACWI Index Fund ACWI 1,201 $2.7 billion Vanguard Total World Stock ETF VT 3,750 $1.2 billion iShares S&P Global 100 Index Fund IOO 102 $1 billion SPDR Global Dow ETF DGT 155 $96.6 million

Two are benchmark-style, with lots of stocks, and two are selective “blue-chip” style. Diversification is not really an issue with any of them, although in that department thousands of stocks would seem to have an edge over 100 or so. On the other hand, concentrated portfolios sometimes can outperform because each component has a heftier weight.

And sometimes not. Since I just used the “P” word, let’s get right to the performance stats. The data below are as of March 31 and are computed using closing market prices of the ETFs.

Name Q1 2012 1 Year 2 Years 3 Years 5 Years iShares MSCI ACWI 11.93% -2.40% 4.15% 18.55% N/A Vanguard Total World 11.79% -3.19% 4.13% 18.58% N/A iShares S&P Global 100 9.75% -2.69% 2.27% 14.60% -3.00% SPDR Global Dow 11.26% -8.54% -0.99% 10.44% -5.63%

A couple of notes about the SPDR Global Dow DGT, -0.62% are in order. First, this ETF was, until May 2, 2011, known as the SPDR DJ Global Titans ETF and benchmarked to the Dow Jones Global Titans Index. So, the track record beyond one year really belongs to a different beast. Second, the Global Dow is equally weighted (rebalanced every September), while the other three are weighted by market capitalization.

The equal weighting explains why the Global Dow sank the most in the year ended March 31, a period in which emerging markets were down about 12%. But the ETF was back in the game in the first quarter of this year when emerging markets rebounded by around 14%. And that explains why the S&P Global 100 ETF lagged the pack in the first period — it has no components from emerging markets. Here is how the four stack up in terms of composition:

Name Number Countries U.S. Weight Emerg. Mkt Wt. Top 10 Weight* iShares MSCI ACWI 48 45.35% 9.72% 9.09% Vanguard Total World 45 41.90% 14.00% 7.70% iShares S&P Global 100 12 50.55% 0.00% 29.32% SPDR Global Dow 15 44.23% 8.45% 8.84%

(*Cumulative weight of the largest 10 holdings in the ETF portfolio.)

S&P Global 100 IOO, -0.55% is highly concentrated in its top 10 holdings. It also is overweight in U.S. stocks, which account for 45.5% of the Dow Jones Global Total Market Index that tracks 12,286 stocks in 76 countries. The Vanguard Total World ETF is underweight U.S. stocks but overweight emerging markets, which constitute 9.7% of the Dow Jones Global TSM Index. Read more: Mexico, Canada put your portfolio on the map.

For all these differences, plus the wide range of component numbers, the four are very similar in terms of volatility, as shown in the table below.

Name 1 Year Return 1 Year Beta* 1 Year Std Dev 1 Year Sharpe iShares MSCI ACWI -2.40% 1.15 25.83% -0.10 Vanguard Total World -3.19% 1.17 26.44% -0.12 iShares S&P Global 100 -2.69% 1.13 25.57% -0.11 SPDR Global Dow -8.54% 1.16 25.95% -0.33

(*Compared to the Dow Jones Global Total Stock Market Index.)

Vanguard Total World’s VT, -0.36% overweighting in emerging markets gives it the highest volatility (though not by much), despite having the most components. The S&P Global 100, with no emerging markets exposure, is the least volatile.

Any of these funds can deliver global equities, but your choice should depend in part on what else is in your portfolio. You want to emphasize emerging markets? Vanguard Total Market tilts in that direction. Maybe you prefer handling emerging markets in a separate vehicle, or avoid them altogether, in which case the S&P Global 100 can represent the developed markets.

Your investing style could affect your choice as well. If you have a size bias, the SPDR Global Dow ETF offers equal weighting, which emphasizes smaller stocks at the expense of larger ones. If you just want the world as it is, the iShares MSCI ACWI ETF ACWI, -0.35% has no marked leanings and thus reflects the global equity market.

John Prestbo is editor and executive director of Dow Jones Indexes, a joint venture of CME Group, Inc., and Dow Jones & Co., Inc., publisher of MarketWatch. Jeffrey Fernandez and Fernando Fernandes contributed research to this report.