Chapter 12: Efficient Markets & Behavioral Finance

Efficient Markets & Behavioral Finance begins by establishing the fundamental difference between investment decisions, where firms seek positive Net Present Value (NPV) through unique assets, and financing decisions, which occur in highly competitive markets where finding positive NPV is challenging. The core theoretical framework presented is the Efficient Market Hypothesis (EMH), which asserts that security prices reflect all available information. The summary details the three forms of market efficiency: weak-form efficiency, implying past prices cannot predict future returns (invalidating technical analysis); semistrong-form efficiency, where prices incorporate all public information (challenging the value of fundamental analysis); and strong-form efficiency, which encompasses private insider information. Key implications include the random walk theory of stock prices, the rationality of passive investing through index funds, and the use of event studies to measure abnormal returns and market reactions to corporate news. The discussion then pivots to evidence contradicting the EMH, exploring anomalies like the momentum effect, reversal patterns, and post-earnings announcement drift. This introduces the field of Behavioral Finance, which explains market inefficiencies through human psychology and limits to arbitrage. We explore cognitive biases such as overreaction, underreaction, and the impact of investor sentiment, alongside Prospect Theory and loss aversion. The chapter also explains why rational investors, or arbitrageurs, cannot always correct mispricing due to risks and costs, illustrated by examples like the Volkswagen short squeeze and the Royal Dutch Shell parity deviation. Finally, the role of agency and incentive problems in creating asset bubbles, particularly regarding the 2008 financial crisis and subprime mortgage market, is examined to highlight how distorted incentives can lead to systemic market failure.