What is home bias and what behavioral factors drive it?

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AcadiFi · Accepted Answer

Home bias is the tendency of investors to over-allocate to domestic assets relative to the global market portfolio. If the US is 55% of global market cap, a mean-variance optimizer ignoring frictions would suggest ~55% US for a global investor, yet typical US investors hold 80%+.

Rational explanations (partial):
1. CURRENCY RISK: Foreign equities carry FX exposure that adds volatility to a USD-based liability portfolio.
2. INFORMATION ASYMMETRY: Domestic firms are easier to research.
3. TAXES: Foreign withholding taxes on dividends (often 15-30%) reduce after-tax returns.
4. REGULATORY FRICTION: Some retirement accounts restrict foreign holdings.

But these explain maybe 40% of observed home bias. The rest is behavioral:

1. FAMILIARITY BIAS: Investors overweight what they know. A Portland resident invests more in Nike, Columbia Sportswear, and Intel — even though global alternatives offer better risk-adjusted returns.

2. AMBIGUITY AVERSION: Ellsberg paradox logic — investors prefer known uncertainty to ambiguous uncertainty. Foreign markets feel 'ambiguous'.

3. PATRIOTISM / SOCIAL IDENTITY: Studies show investors from countries with strong national identity hold more domestic stocks.

4. OVERCONFIDENCE IN DOMESTIC FORECASTS: Investors believe they can predict domestic stocks but not foreign.

Consequences: Home-biased portfolios have roughly 1-2% lower long-run Sharpe ratios than globally diversified equivalents, and can underperform significantly during periods when domestic markets lag (e.g., the 2000-2010 US lost decade when EM and developed-ex-US outperformed).

For CFA Level III, home bias is a classic example of behavioral overrides of mean-variance prescriptions in IPS construction.

What is home bias and what behavioral factors drive it?

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