In this module, we review the behavioral critique of market rationality. In contrast to the presumption that investors are rational, behavioral finance starts with the assumption that they are not. We will examine some of the information-processing and behavioral biases uncovered by psychologists in several contexts. In addition, we will consider alternative, more realistic ways of describing investor preferences.

In this module, we review a number of puzzles related to the aggregate stock market and the cross-section of average stock returns that have been documented in the literature. We examine how the behavioral biases and tendencies discussed in the previous module might result in some of these puzzles observed in financial markets.

In this last brief module, we turn our attention to the behavior of individual investors and review the empirical evidence on how behavioral biases and tendencies we discussed in the previous modules affect individual investor portfolio choice and trading decisions.