11. Behavioral Finance and the Role of Psychology

Summary

Professor Robert Shiller presents behavioral finance as a necessary complement to models that assume people are fully rational. Financial institutions and markets depend on real people, who make predictable errors, can be influenced by how choices are framed, and may exploit others’ weaknesses. Shiller argues, however, that exploitation is limited by reputation, long-term business interests, regulation, and personal morality.

Behavioral Finance Concepts and Market Implications

• Prospect Theory — Daniel Kahneman and Amos Tversky

  • Decisions depend on a psychological reference point, often current wealth. Framing can shift that reference point and change how the same prospect is perceived.
  • The value function is concave for gains (diminishing sensitivity) and convex for losses, with a kink at the reference point. In practice, people can be unusually sensitive to small losses and less responsive to comparable gains.
  • People also distort probabilities: very small probabilities may be treated as zero, while some people instead give them disproportionate weight. This helps explain demand for products such as airline-flight, funeral, and diamond-ring insurance—even when these cover relatively narrow risks rather than major financial exposures.
  • Shiller’s general caution is to prioritize protection against large, consequential risks rather than focus only on small, salient losses.

• Regret and gambling

  • Fear of regretting a decision can lead people to avoid choices or make decisions aimed at preventing future self-blame.
  • Shiller describes gambling as a widespread human behavior that can be addictive and financially destructive. He also argues that some of the same appetite for risk and stimulation is channeled into stock-market activity, which can be productive but may also encourage gambling-like behavior.
  • A 1974 study cited in the lecture found that 61% of U.S. adults had gambled for money at least once that year. Shiller cited compulsive-gambling estimates of 1.1% of men and 0.5% of women.

• Overconfidence

  • Investors and others may overestimate their knowledge, abilities, and capacity to predict outcomes. Shiller links this to overconfidence in prominent CEOs and leaders, which can affect company and market judgments.
  • In a classroom exercise, students gave 90% confidence intervals for three quantities. About 80% included the stated world-population estimate, but only about 10% included the estimates for Earth’s mass and the number of world languages. The exercise illustrates how confidence intervals can be too narrow.
  • Shiller cites Rakesh Khurana’s critique of the “charismatic CEO” search: companies may mistake past success or luck for transferable managerial genius. A celebrated incoming CEO may then disrupt a company they do not understand.
  • Nassim Taleb’s Fooled by Randomness is cited for the broader warning that people often attribute chance outcomes to skill.

• Cognitive dissonance and portfolio decisions

  • Investors may cling to an investment or belief because admitting error is uncomfortable, selectively attending to confirming evidence and overlooking contrary evidence.
  • Research discussed by Shiller found that some mutual-fund investors who held on to poorly performing funds had an exaggerated impression of how the funds had done.
  • In a study of financial-advisor interactions, actors presented portfolios concentrated in different assets—including money-market funds, technology stocks, options, or their employer’s stock. Advisors often accepted the client’s apparent preferences instead of challenging concentration. Only 40% advised an actor heavily invested in their own company’s stock to get out of it.
  • Shiller’s risk-management example is an employee with both a job and life savings tied to one company, such as Ford: a company failure could threaten both income and investments. He argues that an advisor should address this concentration risk, while acknowledging that directly challenging clients may cause them to disengage.

• Anchoring and representativeness

  • Anchoring: In a Kahneman–Tversky experiment, a random wheel number influenced estimates of what percentage of nations belonged to the United Nations, even though the number was irrelevant. In markets, an arbitrary or salient figure can similarly shape judgments under uncertainty.
  • Representativeness heuristic: Investors may overread patterns they recognize. Shiller discusses the Head and Shoulders chart pattern as an example: traders may see it too often or treat it as more predictive than warranted.
  • He describes a hypothetical manipulation in which traders could create a Head and Shoulders pattern in a thinly traded stock and then short it around the apparent sell signal. He says such deliberate market manipulation is illegal and can result in jail.

• Social contagion and market swings

  • Beliefs are influenced by other people and by the “spirit of the times,” not only by individual analysis. Shiller connects herd behavior and shared narratives to large swings in stock markets and other financial activity.

Frameworks and Practical Cautions

• When assessing a risky choice, distinguish gains and losses relative to the relevant reference point and consider whether the choice’s framing is influencing the decision.
• Evaluate probabilities numerically rather than treating them as simply “impossible,” “possible,” or “certain”; be alert to both dismissal and exaggeration of small probabilities.
• Avoid allowing salient but limited risks to displace protection against larger financial threats.
• Question confidence in investment patterns, CEO reputations, and apparent success; outcomes may reflect luck or selective attention.
• Review portfolios for concentration risk, particularly where employment income and investments depend on the same company.
• Be cautious of herd-driven narratives and technical patterns, and do not attempt manipulative trading.

Key Figures and Examples

• A $9.99 price may feel meaningfully cheaper than $10.00, illustrating psychological price framing.
• Shiller gives an airline-crash probability of roughly 1 in 10 million or lower as an example of a risk many people may dismiss or, alternatively, exaggerate.
• He cites diamond-ring insurance for a ring worth roughly $5,000 as an example of coverage focused on a salient, relatively narrow loss.
• The lecture’s classroom estimates, dated February 21, 2011, were world population 6,901,330,581, Earth mass 5.974 × 10²⁴ kilograms, and 6,909 languages according to Ethnologue. These figures served as an overconfidence demonstration, not as financial indicators.

Disclosure

No explicit “not financial advice” disclaimer is given. Shiller presents these points as a lecture on behavioral finance, with examples and research claims discussed in class.

Presenters and Sources Mentioned

Presenter: Professor Robert Shiller.

Sources and researchers cited: Adam Smith (The Theory of Moral Sentiments and The Wealth of Nations); Daniel Kahneman and Amos Tversky; Gerd Gigerenzer; Nick Barberis; Will Goetzmann and co-authors; Sendhil Mullainathan and co-authors; Rakesh Khurana (Searching for a Corporate Savior: The Irrational Quest for Charismatic CEOs); Nassim Nicholas Taleb (Fooled by Randomness); Leon Festinger; Michael Porter and Mark Kramer (shared value); Anna Bernasek (The Economics of Integrity); Emile Durkheim; and technical analyst McGee. Shiller also refers to the DSM-IV, the U.S. Census World Population Clock, Ethnologue, and the Fabozzi finance textbook.