When inferring causal effects from correlational data, a common practice by professional researchers but also lay people is to control for potential confounders. Inappropriate controls produce erroneous causal inferences. I model decision-makers (DMs) who use endogenous observational data to learn actions’ causal effect on payoff-relevant outcomes. Different DM types use different controls. Their resulting choices affect the very correlations they learn from, thus calling for an equilibrium analysis of the steady-state welfare cost of bad controls. I obtain tight upper bounds on this cost. Equilibrium forces drastically reduce it when types’ sets of controls contain one another.

I present a behavioural model of a “data analyst” who extrapolates a fully specified probability distribution over observable variables from a collection of statistical data sets that cover partially overlapping sets of variables. The analyst employs an iterative extrapolation procedure, whose individual rounds are akin to the stochastic regression method of imputing missing data. Users of the procedure’s output fail to distinguish between raw and imputed data, and it functions as their practical belief. I characterize the ways in which this belief distorts the correlation structure of the underlying data generating process—focusing on cases in which the distortion can be described as the imposition of a causal model (represented by a directed acyclic graph over observable variables) on the true distribution.

A group of n “quacks” plays a price-competition game, facing a continuum of “patients” who recover with probability α, whether they acquire a quack's “treatment”. If patients chose rationally, the market would be inactive. I assume, however, that patients choose according to a boundedly rational procedure, which reflects “anecdotal” reasoning. This element of bounded rationality has significant implications. The market for quacks is active, and patients suffer a welfare loss which behaves non-monotonically w.r.t. n and α. In an extended model that endogenizes the quacks' choice of “treatments”, the quacks minimize the force of price competition by offering maximally differentiated treatments. The patients' welfare loss is robust to market interventions, which would crowd out low-quality firms in standard models. Thus, as long as the patients' quality of reasoning is not lifted above the anecdotal level, ordinary competition policies may be ineffective.

I explore the idea that people care about the justifiability of their decisions in the context of two-person extensive games. Each player justifies his strategy s with a belief b of the opponent's strategy which is consistent with the play path and maximally plausible (according to some exogenous criterion). We say that s is justifiable if against the ex post criticism that some other strategy s′ outperforms s against b, the player can argue that playing s′ would have exposed him to similar criticism in the opposite direction. Under a simplicity-based plausibility criterion, this concept implies systematic departures from maximizing behaviour in familiar games.

In standard contract-theoretic models, the underlying assumption is that agent types differ in their preference or cost parameters, and the principal's objective is to design contracts in order to screen this type. We study a contract-theoretic model in which the heterogeneity among agent types is of a “cognitive” nature. In our model, the agent has dynamically inconsistent preferences. Agent types differ only in their degree of “sophistication”, that is, their ability to forecast the change in their future tastes. We fully characterize the menu of contracts which the principal offers in order to screen the agent's sophistication. The menu does not exclude any type: it provides a perfect commitment device for relatively sophisticated types, and “exploitative” contracts which involve speculation with relatively naive types. More naive types are more heavily exploited and generate a greater profit for the principal. Our results allow us to interpret real-life contractual arrangements in a variety of industries.