7.4 International Equity Diversification & Correlation Dynamics

7.4 International Equity Diversification & Correlation Dynamics

1. The Diversification Case

The theoretical argument is a direct application of Markowitz: combining assets whose correlation is below 1.0 reduces portfolio volatility for a given expected return. Different economies experience different shocks, run different policy cycles, and have different industrial structures, so their equity markets should not move in lockstep.

The magnitude of benefit depends entirely on correlation:

$\sigma_p = \sqrt{w_1^2\sigma_1^2 + w_2^2\sigma_2^2 + 2w_1w_2\rho_{1,2}\sigma_1\sigma_2}$

Worked Example: The Correlation Sensitivity

A portfolio allocates 70% to domestic equities ($\sigma = 16%$) and 30% to international developed equities ($\sigma = 18%$). The weighted-average volatility, which ignores diversification, is $0.70(16) + 0.30(18) = 16.6%$.

At $\rho = 0.85$ — roughly the level observed between developed markets in recent decades — the volatility reduction is meaningful but modest. At the $\rho \approx 0.40$ levels observed in the 1970s and 1980s, the benefit was far larger. This decline in the benefit is the central empirical development in this topic.

2. Home Bias

Home bias is the well-documented tendency of investors in every country to hold far more domestic equity than global market weights imply. US investors typically hold 70–80% or more of their equity in US securities, against a US share of global equity capitalization that has generally been in the 40–60% range.

Explanations offered:

• Liability matching. An investor's liabilities are denominated in domestic currency, so domestic assets carry a genuine matching advantage. This is the most defensible justification.
• Currency risk aversion. Unhedged foreign holdings add exchange-rate volatility.
• Information asymmetry and familiarity. Investors believe they understand domestic companies better — partly rational, partly the familiarity heuristic covered in behavioral finance.
• Costs, taxes, and restrictions. Withholding taxes, custody costs, and institutional mandates.
• Implicit domestic exposure. Large domestic multinationals already generate substantial foreign revenue, so geographic exposure exceeds the listing venue.

The consultant's balanced position: home bias is partly rational, particularly for liability matching, but the magnitude typically observed exceeds what those justifications support. The last argument — that multinationals provide sufficient international exposure — deserves particular scrutiny: revenue geography is not the same as return behavior. A US-listed multinational still trades with US market sentiment, US interest rates, and US sector dynamics.

3. The Risks of International Allocation

4. Currency: A Separable Decision

A critical framing point the exam tests: holding international equities and bearing currency risk are two distinct decisions. An investor can hold foreign equities and hedge the currency, partially hedge, or leave it unhedged.

An unhedged return is approximately:

$R_{unhedged} \approx R_{local} + R_{currency}$

Considerations:

• Currency is widely regarded as having near-zero long-run expected return, so it adds volatility without a reliable premium. This is the primary argument for hedging.
• Over long horizons, purchasing power parity exerts a weak pull that partially mutes currency effects — but "long" here means decades, not client planning horizons.
• Foreign currency exposure can be diversifying for equity portfolios: currencies such as the US dollar, Japanese yen, and Swiss franc have historically appreciated during global risk-off episodes, which can cushion equity drawdowns for non-US investors.
• Hedging has real costs: forward points reflecting interest-rate differentials, plus operational complexity and cash-flow management for margin.

Common practice is to hedge currency exposure in international fixed income — where currency volatility can exceed the volatility of the underlying bonds, overwhelming the asset class's role in the portfolio — and to hedge international equity partially or not at all, since currency volatility is small relative to equity volatility.

5. Changing Correlations Across Countries, Regions, and Sectors

The blueprint explicitly requires candidates to describe changes in correlations between equity sectors, countries, and regions.

The documented trend is upward. Developed-market equity correlations that averaged roughly 0.4–0.5 in the 1970s and 1980s have generally run in the 0.7–0.9 range in recent decades. The drivers are structural:

1. Globalization of revenue. Index-weight companies increasingly earn revenue across many countries, so their fortunes converge regardless of listing venue.
2. Integrated capital markets. Capital moves freely, and global investors reprice all markets on the same information.
3. Synchronized monetary policy. Major central banks now respond to overlapping global conditions, and global liquidity conditions dominate.
4. Common global factors. Shared exposure to growth, rates, and risk appetite dominates local idiosyncrasy.
5. Passive and ETF flows. Broad index vehicles trade whole markets as single instruments.

Correlation asymmetry is the crucial refinement. Correlations are not stable across market conditions: they rise sharply in drawdowns. In the 2008 crisis and the March 2020 shock, cross-country equity correlations converged toward 1.0. Diversification therefore delivers least protection precisely when it is most needed — a phenomenon sometimes called "diversification failing when you need it most," and a central argument for holding genuinely different risk exposures (duration, cash, certain alternatives) rather than relying solely on geographic breadth within the equity asset class.

Sector versus country effects. Historically, country membership explained more of a stock's return variation than its industry. That relationship has shifted substantially: industry and factor composition now explain a comparable or larger share for developed markets. A practical consequence is that a "diversified" international allocation that is heavily weighted toward the same global technology and growth names as the domestic index provides far less true diversification than its geographic labelling suggests. Look through to the factor and sector exposure, not the country label.

Where the argument still holds. Emerging market correlations to developed markets remain meaningfully lower than developed-to-developed correlations, and smaller-capitalization international equities are more locally driven than international large caps. The diversification case has weakened at the large-cap developed level; it has not disappeared, and it remains strongest in exactly the segments most investors underweight.