Diversification is often presented as the most basic principle of investing: hold many different assets and the risks cancel out. But the degree to which risks actually cancel out depends entirely on how those assets relate to each other — their correlation.
Understanding correlation is the difference between a portfolio that is genuinely diversified — where poor performance in one part is cushioned by stability or gains in another — and one that merely appears diverse but will fall sharply in the same scenarios, at the same times.
This article explains correlation, how to use it to build better portfolios, and why international investors are often better placed than domestic investors to achieve genuine diversification.
What Is Correlation?
Correlation is a statistical measure of how two variables move in relation to each other. In investment terms, it measures how the returns of two assets tend to move together.
Correlation is expressed on a scale from -1 to +1:
- +1.0 (perfect positive correlation): The two assets always move in the same direction by the same proportion. Holding both provides no diversification benefit.
- 0 (zero correlation): The movements of the two assets are completely unrelated. Holding both provides full diversification benefit.
- -1.0 (perfect negative correlation): The two assets always move in exactly opposite directions. Holding both theoretically eliminates all variance. (In practice, no real investment pair exhibits perfect negative correlation over sustained periods.)
Most real investment pairs fall between 0 and +1 — they tend to move in the same direction more often than not, but not perfectly. The closer to zero, the better the diversification.
The Mathematics of Diversification
Harry Markowitz's Modern Portfolio Theory (1952) — one of the few genuine theoretical breakthroughs in investment finance — demonstrated mathematically that combining assets with less-than-perfect correlation reduces portfolio risk without proportionally reducing expected returns.
The key insight: You can achieve the same expected return at lower risk by holding two assets with low correlation, compared to holding either asset alone.
Example: Asset A has an expected return of 8% and volatility of 15%. Asset B has an expected return of 8% and volatility of 15%. If A and B have a correlation of +1.0, combining them 50/50 reduces nothing — you still have 15% volatility. If they have a correlation of 0.0, the 50/50 combination has expected volatility of approximately 10.6% — with the same 8% expected return. If they have a correlation of -1.0, the 50/50 combination has zero volatility and 8% certain return (a theoretical extreme never achieved in practice).
This is why asset allocation — choosing assets with low correlations — matters far more than any other investment decision, including the choice between individual securities.
Correlation Between Major Asset Classes
The historical correlation between major asset classes provides the building blocks for portfolio construction.
Equities and government bonds (developed markets)
Over long historical periods (pre-2000 data), equities and developed market government bonds exhibited near-zero or mildly positive correlation. Since 2000, they have often been negatively correlated — bond prices rising when equities fall, and vice versa.
This negative correlation underpins the 60/40 equity/bond portfolio. When equities fell sharply in 2002–2003 and 2008–2009, government bonds rose in value, cushioning the blow.
However, in 2022, this relationship broke down. As central banks raised interest rates aggressively, both equities and bonds fell simultaneously — a phenomenon called "correlation breakdown" or "regime change". The 60/40 portfolio suffered its worst year in decades as both components fell together.
This illustrates that correlation is not constant — it varies across economic regimes and can fail precisely when diversification is most needed.
Equities and corporate bonds (high yield)
High-yield corporate bonds — issued by companies with below-investment-grade credit ratings — are significantly positively correlated with equities. Both are driven by economic growth expectations and corporate profitability. In the 2008 crisis, both fell severely. The diversification benefit of adding high yield to an equity portfolio is limited.
Equities and commodities
Broad commodity indices have historically had low correlation with equities, making them useful portfolio diversifiers. However:
- Individual commodities (oil, gold, agricultural commodities) vary considerably in their correlation to equities
- Gold specifically has shown periods of negative equity correlation and is widely used as a crisis hedge
- Energy commodities are more positively correlated with equities through their link to global economic activity
Equities and real estate (REITs)
Listed real estate investment trusts are moderately to highly correlated with equities (correlation typically 0.6–0.8) because they trade on stock exchanges and are priced according to market sentiment as well as underlying property values. Unlisted direct property has lower correlation to equities — but is illiquid.
Developed market equities and emerging market equities
Higher correlation than many investors expect: approximately 0.7–0.8 over recent decades. Both tend to fall in global risk-off episodes. Geographic diversification across developed markets (US, Europe, Japan) provides more genuine risk reduction than adding emerging markets to a developed market portfolio.
Equities and gold
Gold has historically had near-zero or mildly negative correlation with equities. It specifically tends to outperform in:
- Periods of high inflation
- Periods of dollar weakness
- Geopolitical crises
- Periods of systemic financial stress
Gold does not generate income, is not productive, and has significant storage and transaction costs. But its low correlation with equities gives it a genuine role as a portfolio hedge for a small allocation (3–7%).
Equities and trend-following (managed futures)
Managed futures strategies — which systematically take long and short positions in equity, bond, currency, and commodity markets based on price momentum — have historically shown near-zero or negative correlation with equity markets. In equity crises (2000–2002, 2008), managed futures typically performed strongly. Available through UCITS funds and some ETFs.
Building a Genuinely Diversified Portfolio
A portfolio that combines assets with low or negative correlations can achieve a better risk-return trade-off than any individual component. In practice:
The two-asset base
Global equities (MSCI ACWI) + global government bonds (GBP hedged) provides a historically reasonable diversification backbone, with equity/bond correlation typically near zero or mildly negative over long periods.
The 2022 experience shows this can break down — adding further diversifiers is valuable.
Adding real assets
Global REITs and infrastructure assets tend to have moderate positive correlation with equities but also provide inflation linkage. A 10–15% allocation to real assets in a well-diversified portfolio provides differentiated return drivers.
Adding gold or commodities
A 3–7% allocation to gold provides crisis diversification. A broader commodity allocation (5–10%) adds inflation sensitivity.
Adding alternatives
Trend-following strategies, global macro funds, and absolute return strategies have historically provided genuine diversification — their returns have been largely uncorrelated with traditional equity and bond markets, particularly in crises. Available through UCITS alternative funds for international investors.
An illustrative diversified portfolio (medium risk):
| Asset class | Allocation | Role |
|---|---|---|
| Global developed equity (UCITS ETF) | 40% | Growth engine |
| Emerging market equity (UCITS ETF) | 10% | Higher-risk growth, partial geographic diversification |
| Global government bonds (GBP hedged UCITS ETF) | 20% | Defensive diversifier, crisis hedge |
| Global investment-grade corporate bonds | 5% | Income, moderate risk |
| Global REITs (UCITS ETF) | 5% | Real asset exposure, inflation linkage |
| Infrastructure | 5% | Stable income, low equity correlation |
| Gold | 5% | Crisis hedge, inflation protection |
| Trend-following / alternatives | 5% | Crisis diversifier, low equity correlation |
| Cash | 5% | Liquidity, optionality |
Expected portfolio volatility (standard deviation) would be significantly lower than a single global equity ETF, while expected returns would be only modestly lower.
Geographic Diversification for International Investors
One of the most important and most overlooked forms of diversification is geographic. Many domestic investors — particularly UK investors — are significantly overweight their home country relative to its share of global market capitalisation.
The UK represents approximately 4% of global equity market capitalisation (as of 2026) but a typical UK retail investor holds 30–50% of their equity portfolio in UK stocks. This home-country bias — driven by familiarity, comfort, and historical platform design — represents a genuine diversification failure.
For internationally mobile investors living outside their home country, geographic diversification happens more naturally. An investor living in the UAE who has previously lived in the UK and currently works in a global company may genuinely hold assets across three continents. This is genuine geographic diversification that domestic investors rarely achieve.
The globally diversified portfolio — across US, European, Asia-Pacific, and emerging market equities — ensures that localised economic downturns (UK recession, Chinese slowdown, European banking crisis) do not devastate the whole portfolio.
The Limits of Correlation Data
A cautionary note: correlation is measured from historical data and is not stable over time.
- Correlations between assets can change dramatically during different economic regimes
- Crisis periods tend to produce correlation convergence (assets that normally have low correlations move together)
- Short historical periods can produce misleading correlations
Investors should use correlations as a guide, not a guarantee. Building in multiple sources of genuine diversification — asset class, geography, factor, strategy — provides more resilience than relying on any single pair of low-correlated assets.
Compliance Caveats
All investments can fall in value as well as rise. Historical correlations between assets are not guaranteed to persist. Diversification reduces but does not eliminate investment risk. The portfolio examples in this article are illustrative and do not constitute personal financial advice. The appropriate allocation for any individual investor depends on their circumstances, objectives, risk tolerance, and time horizon.
How Global Investments Can Help
At Global Investments, we use quantitative correlation analysis as part of our portfolio construction process for internationally mobile clients. We look beyond superficial diversification — multiple funds, multiple providers — to ensure genuine independence of return drivers. If you would like a correlation analysis of your existing portfolio or a genuinely diversified global portfolio built from scratch, 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.