Global Diversification Dominance
Home bias is always wrong — own the world, not your postcode
The DMS 125-year dataset across 35 countries provides unambiguous evidence that global diversification reduces portfolio risk without sacrificing expected return. No individual country has reliably predicted its own future outperformance — the markets that looked dominant at any given time (Japan in 1989, the UK in 1900, the US in 2024) were often followed by periods of underperformance. Owning the global market-cap-weighted index eliminates the single-country concentration risk that has destroyed wealth in multiple historical episodes.
Home bias — the tendency of investors to overweight their domestic market — is systematically harmful for most countries. Most investors are already economically exposed to their home country through their employment, housing, and local economy; adding a portfolio overweight to the same economy compounds that concentration. The people who most need international diversification are those who already live and work in a country: a British worker with a UK-listed employer, a UK mortgage, and a UK-heavy pension fund is three times over-exposed to UK economic outcomes.
The specific policy application Staunton addresses is the UK government's pressure on pension default funds to increase UK equity allocations. He calls this directly wrong — not merely suboptimal, but a policy error that will harm the retirement outcomes of the default-fund investors who are least equipped to make their own allocation decisions. The correct answer, validated by 125 years of data across 35 countries, is maximum feasible diversification at minimum cost.
- Diversifying globally reduces portfolio risk; no single country has reliably outperformed over 125 years on an ex-ante basis.
- Most investors are already overexposed to their home economy through employment, housing, and human capital — portfolio home bias compounds this concentration.
- The US is the world's least concentrated major equity market by sector — but that does not make a US-only allocation globally diversified.
- Government-mandated home bias in pension default funds harms the investors least able to override the default.
- The cost of diversification has fallen to near-zero for retail investors through global index funds — there is no longer a cost-efficiency argument for home bias.
- Measure your total economic exposure to your home countryBefore assessing portfolio allocation, account for all sources of home-country exposure: employment income, property value, business ownership, and any country-specific pension entitlements. This total exposure is your de facto home-country position before any investment decision.Pro tipFor most employed homeowners in a single country, the home-country exposure from non-portfolio sources already exceeds a reasonable concentration limit. Portfolio allocation should compensate, not compound.
- Choose a global market-cap-weighted equity fund as the core holdingA global index fund — covering developed and emerging markets weighted by market capitalization — is the single most diversified, lowest-cost implementation of the evidence base. It automatically weights toward markets that grow and away from markets that shrink, eliminating active country-allocation decisions.Pro tipStaunton and Marsh personally use Vanguard global index funds. They acknowledge lower-cost alternatives (Invesco global) but note that size-related liquidity risks must be weighed against the cost differential.WarningSome 'global' funds sold to retail investors have significant home-country tilts built in by fund construction choices — check the geographic breakdown, not just the fund name.
- Resist home-bias tilts from any source — including government policyActive pressure to add domestic equity allocations — from financial advisers, employers, government policy, or personal affinity — should be evaluated against the diversification evidence. The question is: what does this tilt do to concentration risk and expected return relative to the global baseline?Pro tipNorway provides the institutional template: the Norwegian Pension Fund Global explicitly allocates zero to Norwegian equities — domestic exposure is managed through a separate domestic fund — precisely to avoid compounding the economic exposure of Norway's citizens.WarningUK auto-enrollment default funds are currently being pushed toward UK equity allocations by government policy. Staunton explicitly calls this wrong. Investors who can override the default should do so.
- Hold the global allocation through country-performance cyclesGlobal diversification will consistently underperform the best-performing single country in any given period. The US outperformed global in the 2010s; Japan was the world's dominant market in the 1980s. The discipline of the framework is to hold through these cycles without reallocating toward the current winner.Pro tipThe 'flow of markets' chart from the DMS data — showing how Japan bubbled up and then collapsed in global weight, how the UK declined from 25% to 4% of world market cap — is the empirical argument for never making permanent country concentration bets.WarningEven investors who correctly applied the diversification framework and added international exposure in the 1990s were worse off than US-concentrated investors for the following two decades — correct decisions can produce suboptimal outcomes over long periods.
- Minimize cost as the primary portfolio leverOnce globally diversified, the only reliable source of return improvement is fee reduction. The alpha from active country allocation is uncertain and historically negative after costs. The alpha from index fund adoption is certain, permanent, and compounds at the full rate of the underlying equity premium.
When the Norwegian Petroleum Fund was established, one of its first governance decisions was to allocate zero to Norwegian equities. Norway would own 1.5% of every listed company in the world except Norwegian ones, which were handled through a separate domestic fund. The logic was that Norwegian citizens were already economically exposed to Norway — adding a portfolio overweight would compound the concentration.
At the start of the 20th century, the UK represented approximately 25% of world equity market capitalization. By the time of this episode, that share had fallen to roughly 4%. British investors who held UK-heavy portfolios throughout this period experienced significant erosion of their global purchasing power relative to a globally diversified alternative.
Japan grew to represent approximately 40-45% of global equity market capitalization at the peak of its bubble in 1989, making it the world's dominant market. Investors who chased this dominance and concentrated in Japanese equities were badly hurt by the subsequent 30-year period of stagnation.
US institutional investors began adding international equity exposure from the 1990s onward, motivated by the same global diversification evidence the DMS database provides. Through the 2010s, US equities dramatically outperformed international equities — making the diversification decision look wrong in hindsight.
Staunton and Marsh arrived at this conclusion through the construction of the DMS world index itself. When they began, the standard finance textbook comparison was US vs. US bonds. Extending the dataset to 35 countries revealed that individual-country returns are highly variable, that the US was the best-performing major market in the 20th century, and that no investor could have known ex ante which country would win. The implication — maximize global diversification — flows directly from the data rather than from any theoretical prior. Both speakers personally invest via Vanguard global index funds, which they cite as the practical implementation of the framework.