Barberis & Thaler (2002) - A Survey of Behavioral Finance

Overview

Barberis and Thaler's 2002 survey, written for the Handbook of the Economics of Finance, is the definitive map of behavioral finance. Its contribution is organizational: the field's many findings collapse into two pillars — limits to arbitrage and psychology — and every anomaly in the literature is a consequence of one, the other, or their interaction.

Pillar One: Limits to Arbitrage

Traditional finance assumed mispricing is self-correcting: smart money buys cheap and sells dear until prices are right. The survey documents why the correction is weaker in practice. Fundamental risk (the hedge is never perfect), noise trader risk (mispricing can deepen before it corrects), and implementation costs (fees, short-sale constraints, capital withdrawal) all prevent arbitrageurs from fully closing gaps. The twin share classes of Royal Dutch and Shell — identical cash flows trading at persistent discounts — are the canonical case.

Pillar Two: Psychology

The second pillar catalogues the systematic biases in beliefs and preferences that create mispricing in the first place. Belief biases include overconfidence, conservatism, and representativeness — investors overextrapolating from small samples. Preference biases center on prospect theory: loss aversion, reference dependence, and probability weighting that make risk attitudes differ sharply from expected-utility predictions.

Putting Them Together

The two pillars work in tandem: psychology explains why prices depart from fundamentals; limits to arbitrage explains why nobody fully fixes them. Momentum, value, and long-term reversal anomalies each trace to specific belief or preference biases combined with specific arbitrage frictions.

Why It Matters

The survey legitimized behavioral finance as a serious research program and gave practitioners a vocabulary for persistent inefficiencies. Its two-pillar structure remains the clearest lens for evaluating any claimed anomaly: identify the bias that creates it and the friction that preserves it.

Key Takeaways

• Anomalies require both pillars: a bias without a friction corrects away; a friction without a bias has nothing to preserve.
• Noise trader risk explains why mispricing deepens — arbitrage has limits, not just costs.
• Prospect theory preferences drive the risk puzzles that expected utility cannot describe.