In 1976, Vanguard launched the first index mutual fund available to retail investors. Its founder, John Bogle, was ridiculed by the investment industry — the idea of simply matching the market rather than trying to beat it seemed defeatist, even un-American. Fifty years later, the evidence has vindicated Bogle comprehensively. Index funds and ETFs now manage more assets than active funds in the United States, and the case for passive management has become one of the most thoroughly tested propositions in all of finance.
This article examines the evidence, explains how index funds work, and considers what they mean for internationally mobile investors managing global portfolios.
What Is an Index Fund?
An index fund is a pooled investment vehicle that tracks a financial index — the FTSE 100, the S&P 500, the MSCI World — by holding the underlying securities in proportion to their index weight. If Company X represents 2% of the S&P 500, an S&P 500 index fund holds 2% of its assets in Company X.
The goal is not to beat the market but to match it, less fees. Because the portfolio changes only when the index changes — rebalancing on index additions and deletions — turnover is low, transaction costs are minimal, and management fees are a fraction of active fund charges.
Index funds are available as traditional mutual funds (priced once daily) and as exchange-traded funds (ETFs) that trade continuously throughout the trading day.
The Performance Evidence
The evidence on active versus passive management is extensive and broadly consistent across time periods, asset classes, and geographies.
The S&P SPIVA Reports
S&P Global's SPIVA (S&P Indices Versus Active) Scorecard is published twice yearly across multiple global markets. The headline finding, as of 2026, is stark:
- Over a 15-year period to end 2025, approximately 88% of US large-cap active funds underperformed the S&P 500 after fees
- In European equity funds, over 85% underperformed their benchmark over the same period
- In global emerging markets, the figure is over 75%
- Bond funds fare no better: across most fixed income categories, 70–90% of actively managed funds underperform over a 15-year horizon
The pattern is consistent: over short periods (one year), some active managers beat the index. Over longer periods, the proportion dwindles. Over 15–20 years, outperformers become rare.
Survivorship Bias
One complication in measuring active performance is survivorship bias: funds that underperform tend to be closed or merged, so historical averages overstate typical active performance. When closed funds are included in the analysis, active performance looks even worse.
SPIVA accounts for this by including all funds that existed at the start of each measurement period. Even so, the results are sobering for active managers.
Persistence of Outperformance
A critical question is whether the minority of active funds that do outperform over one period continue to do so in subsequent periods. The evidence suggests not.
Research consistently shows that top-quartile performance in one period does not predict top-quartile performance in the next. In other words, past outperformance has little predictive value. Selecting active funds based on historical returns is therefore a poor strategy.
This is the heart of the passive case: even if some managers can beat the market (and some can, at least for periods), identifying them in advance is extremely difficult. You are essentially betting on your ability to predict who will outperform — and the evidence suggests this skill is rare even among professional fund selectors.
Why Active Management Underperforms: The Arithmetic
The underperformance of active management is partly a mathematical inevitability.
Before costs, all investors in aggregate must earn the market return. They collectively hold all the securities in the market, so the average result must equal the market return. But active managers charge higher fees. After costs, the average active manager must therefore earn less than the market — this is sometimes called the arithmetic of active management, articulated clearly by Nobel laureate William Sharpe.
This does not mean no active manager can beat the market — clearly some do. It means the average active manager cannot, by definition. And identifying in advance which managers will beat the market has proved extraordinarily difficult.
Additional factors that disadvantage active managers:
- Transaction costs: High portfolio turnover generates trading costs. Studies suggest average active equity fund turnover of 50–100% annually
- Tax costs: Frequent trading realises capital gains, creating tax liabilities in many jurisdictions
- Management fees: Typical actively managed equity funds charge 0.75–1.5% per year. A global index fund might charge 0.10–0.20%
- Behavioural drag: Active managers, like all investors, are subject to behavioural biases that affect decision-making
The fee difference alone — compounded over 20 years — is dramatic. The difference between a 1.2% annual charge and a 0.15% annual charge on a £250,000 portfolio is approximately £85,000 over 20 years, assuming 7% gross annual returns.
How Index Funds Are Constructed
Understanding index construction helps investors make better choices.
Market-capitalisation weighting is the most common approach. The largest companies receive the highest weights. A market-cap weighted global index naturally over-weights the US, which represents approximately 65% of global market capitalisation as of 2026. Critics argue this is momentum-driven — it automatically over-weights whatever has risen most.
Equal weighting gives each security the same weight regardless of size. This provides greater exposure to smaller companies but requires frequent rebalancing and has higher costs.
Fundamental weighting weights securities by economic metrics such as earnings, dividends, or book value rather than price. This is the basis of many "smart beta" strategies.
Float-adjusted indices exclude shares not freely available for trading, such as government-held stakes or shares locked up in private ownership. Most major indices are float-adjusted.
When choosing an index fund, understanding what the index actually measures is essential. Two "global equity" index funds may hold very different portfolios depending on which index they track.
What Index Funds Can and Cannot Do
Index funds are not a panacea.
They cannot outperform the market — by design, a market-cap index fund matches the market, less fees. In a rising market, this is excellent. In a falling market, the fund falls broadly in line with the market.
They do not protect against systematic risk. A global equity index fund fell approximately 34% during the COVID crash of March 2020, recovered strongly, but the experience illustrated that index funds are fully exposed to market downturns. Diversification across asset classes — not just within equities — provides more meaningful risk reduction.
They track whatever they track. An S&P 500 index fund concentrates over 65% of its assets in US equities. A global index fund by MSCI concentrates significantly in large-cap developed-market stocks. Investors who believe they want "global diversification" through a single fund may find their exposure is more concentrated than they expected.
Transaction costs are not zero. ETF index funds have bid-ask spreads and brokerage commissions. For investors making regular monthly contributions, these costs can be meaningful.
Index Funds and International Investors
For internationally mobile investors, index funds offer particular advantages:
Simplicity: Managing a global portfolio from abroad is administratively demanding. A small number of index funds covering global equities, bonds, and perhaps property reduces administrative burden significantly.
Portability: Widely available UCITS index ETFs trade on major exchanges and are accessible from most international platforms. They do not require a specific country relationship.
Transparency: Monthly disclosure of holdings means investors always know what they own — useful when completing foreign asset declarations required by many tax authorities.
Tax efficiency: Low turnover means lower capital gains distributions. Accumulating share classes allow earnings to compound without generating annual income tax events in many jurisdictions.
However, international investors must still navigate jurisdiction-specific rules:
- The UK Reporting Fund Status of a fund determines whether gains are taxed as income or capital gains for UK residents
- German Vorabpauschale (pre-tax) rules impose a notional annual income tax on accumulating funds held by German residents
- French PFU (prélèvement forfaitaire unique) applies at 30% to dividends and capital gains on investment funds
- Offshore fund regimes in various jurisdictions may penalise holdings in non-locally-approved funds
Always seek local tax advice before investing in index funds from a new country of residence.
Building an Index Fund Portfolio
The academic research supports remarkably simple portfolios.
The two-fund global portfolio: A single global equity index ETF (e.g., tracking MSCI ACWI) combined with a global aggregate bond ETF. The equity allocation determines the risk level. Research by Vanguard and others suggests this two-fund approach produces returns comparable to much more elaborate portfolios, with less complexity and lower costs.
The three-fund portfolio: Extending the two-fund approach by separating developed and emerging market equities. MSCI World (developed markets) plus MSCI Emerging Markets plus global bonds. This allows you to adjust your emerging market allocation independently.
Adding inflation protection: For investors with long retirements ahead, adding an allocation to inflation-linked bonds or commodity ETFs provides a hedge against unexpected inflation.
The appropriate equity/bond split depends on risk tolerance, time horizon, and income needs. Common rules of thumb (e.g., "your age in bonds") are crude but provide a starting point for discussion.
The Limits of Passive
Passive investing has a potential collective action problem: if all investors become passive, prices lose their information content. Active managers perform a price discovery function. If passive investing continues to grow, some argue this mechanism degrades.
Academic debate on this point continues. In practice, active management remains widespread and the concerns about passive crowding effects appear largely theoretical at current penetration levels.
There are also asset classes where passive investing is more difficult or less available:
- Private equity, private credit, infrastructure: No liquid ETF can provide genuine exposure to these illiquid markets
- Hedge fund strategies: Cannot be replicated by index funds
- Specialist fixed income: Some bond markets are too illiquid for straightforward index replication
For investors with sophisticated needs, a core of passive index funds supplemented by carefully selected active or alternative strategies may be appropriate. This is the basis of core-satellite investing.
Compliance Caveats
Past performance is not a reliable indicator of future results. Index funds, like all investments, can fall in value as well as rise, and you may receive back less than you invest.
The tax treatment of index funds and ETFs varies by jurisdiction and individual circumstances. This article does not constitute personal financial or tax advice. Rules governing offshore funds, reporting status, and fund taxation change and you should seek professional advice appropriate to your circumstances before investing.
How Global Investments Can Help
At Global Investments, we help internationally mobile clients build robust, cost-efficient investment portfolios using evidence-based principles. We can advise on the appropriate index fund structure for your jurisdiction, select tax-efficient investment wrappers, and build a globally diversified portfolio tailored to your risk profile and long-term objectives.
If you are uncertain whether a passive, active, or blended approach is most appropriate for your circumstances, our advisers can provide a clear, independent assessment. Contact us to arrange a consultation.
This article is for general information only and does not constitute financial, legal or tax advice. Rules, prices and regulations change; verify current requirements with a qualified adviser before acting.