Why popular index combinations offer less spread than you would think.
More funds feel like more diversification. Often they are the opposite. Hold two ETFs that buy the same companies, and you have doubled a single risk rather than spread it.
Diversification is not measured by the number of funds, but by the number of risks they spread.
Many investors pair MSCI World with the S&P 500 in the belief that this makes them more broadly diversified. In truth they create a substantial concentration risk: roughly 65-70 percent of the MSCI World positions are also held in the S&P 500.
More ETFs do not automatically mean more diversification. What matters is which markets the ETFs cover, not how many ETFs sit in the portfolio.
| Characteristic | MSCI World | S&P 500 |
|---|---|---|
| Countries | 23 developed markets | United States only |
| Positions | ~1,400 | ~500 |
Roughly 65-70 percent of the positions in the MSCI World are also held in the S&P 500. Both indices are heavily dominated by US mega-caps.
A sensible combination would be, for example, MSCI World + MSCI Emerging Markets, or FTSE All-World as a single-ETF solution. What matters is that the indices cover different markets and regions.
Not directly, but it creates a concentration risk. When US tech stocks fall, both ETFs are hit at the same time. The expected return is no worse, but the risk is higher than with genuine spread.
| US share |
| ~70 percent |
| 100 percent |
| Top 10 weighting | ~25 percent | ~35 percent |
| Emerging markets | No | No |
The ten largest positions in both indices are nearly identical: Apple, Microsoft, Amazon, Nvidia and other US mega-caps dominate each of them.
Real diversification means the holdings are spread across different sources of risk:
A single MSCI World covers only large and mid caps in developed markets: no emerging markets and no small caps.
| Combination | Coverage | Overlap |
|---|---|---|
| MSCI World + S&P 500 | Developed markets (US doubled up) | ~70 percent |
| MSCI World + MSCI EM | Developed and emerging markets | 0 percent |
| FTSE All-World (1 ETF) | Developed and emerging markets | n/a |
| MSCI ACWI IMI (1 ETF) | All countries + small caps | n/a |
Single-ETF solutions such as FTSE All-World or MSCI ACWI are the simplest and most effective choice for most investors. No rebalancing, no overlap, maximum spread.
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