Many people believe in the "Law of Small Numbers," exaggerating the degree to which a small sample resembles the population from which it is drawn. To model this, I assume that a person exaggerates the likelihood that a short sequence of i.i.d. signals resembles the long-run rate at which those signals are generated. Such a person believes in the "gambler's fallacy", thinking early draws of one signal increase the odds of next drawing other signals. When uncertain about the rate, the person over-infers from short sequences of signals, and is prone to think the rate is more extreme than it is. When the person makes inferences about the frequency at which rates are generated by different sources --- such as the distribution of talent among financial analysts --- based on few observations from each source, he tends to exaggerate how much variance there is in the rates. Hence, the model predicts that people may pay for financial advice from "experts" whose expertise is entirely ...

We develop a model of reference-dependent preferences and loss aversion where “gain-loss utility” is derived from standard “consumption utility” and the reference point is determined endogenously by the economic environment. We assume that a person's reference point is her rational expectations held in the recent past about outcomes, which are determined in a personal equilibrium by the requirement that they must be consistent with optimal behavior given expectations. In deterministic environments, choices maximize consumption utility, but gain-loss utility influences behavior when there is uncertainty. Applying the model to consumer behavior, we show that willingness to pay for a good is increasing in the expected probability of purchase and in the expected prices conditional on purchase. In within-day labor-supply decisions, a worker is less likely to continue work if income earned thus far is unexpectedly high, but more likely to show up as well as continue work if expected income is high.

Recent models of procrastination due to self-control problems assume that a procrastinator considers just one option and is unaware of her self-control problems. We develop a model where a person chooses from a menu of options and is partially aware of her self-control problems. This menu model replicates earlier results and generates new ones. A person might forgo completing an attractive option because she plans to complete a more attractive but never-to-be-completed option. Hence, providing a nonprocrastinator additional options can induce procrastination, and a person may procrastinate worse pursuing important goals than unimportant ones.

Psychological research indicates that people have a cognitive bias that leads them to misinterpret new information as supporting previously held hypotheses. We show in a simple model that such confirmatory bias induces overconfidence: given any probabilistic assessment by an agent that one of two hypotheses is true, the appropriate beliefs would deem it less likely to be true. Indeed, the hypothesis that the agent believes in may be more likely to be wrong than right. We also show that the agent may come to believe with near certainty in a false hypothesis despite receiving an infinite amount of information.

We examine how principals should design incentives to induce time-inconsistent procrastinating agents to complete tasks efficiently. Delay is costly to the principal, but the agent faces stochastic costs of completing the task, and efficiency requires waiting when costs are high. If the principal knows the task-cost distribution, she can always achieve first-best efficiency. If the agent has private information, the principal can induce first-best efficiency for time-consistent agents, but often cannot for procrastinators. We show that second-best optimal incentives for procrastinators typically involve an increasing punishment for delay as time passes.

Departures from self-interest in economic experiments have recently inspired models of “social preferences”. We design a range of simple experimental games that test these theories more directly than existing experiments. Our experiments show that subjects are more concerned with increasing social welfare—sacrificing to increase the payoffs for all recipients, especially low-payoff recipients—than with reducing differences in payoffs (as supposed in recent models). Subjects are also motivated by reciprocity: They withdraw willingness to sacrifice to achieve a fair outcome when others are

People exaggerate the degree to which their future tastes will resemble their current tastes. We present evidence from a variety of domains which demonstrates the prevalence of such projection bias, develop a formal model of it, and use this model to demonstrate its importance in economic environments. We show that, when people exhibit habit formation, projection bias leads people to consume too much early in life, and to decide, as time passes, to consume more—and save less—than originally planned. Projection bias can also lead to misguided purchases of durable goods. We discuss a number of additional applications and implications.