Rationality leads people to imitate those with similar tastes but different information. But people who imitate common sources develop correlated beliefs, and rationality demands that later social learners take this correlation into account. This implies severe limits to rational imitation. We show that (i) in most natural observation structures besides the canonical single-file case, full rationality dictates that people must “anti-imitate” some of those they observe; and (ii) in every observation structure full rationality dictates that people imitate, on net, at most one person and are imitated by, on net, at most one person, over any set of interconnected players. We also show that in a very broad class of settings, any learning rule in which people regularly do imitate more than one person without anti-imitating others will lead to a positive probability of people converging to confident and wrong long-run beliefs.

We model a dynamic, competitive market, where in every period, risk-neutral traders trade a one-period bond against an infinitely lived asset, with limited short-selling of the long-term asset. Traders lack structural knowledge and use different “incomplete theories,” all of which give statistically correct beliefs about next period's market price of the long-term asset. The more theories there are in the market, the higher is the equilibrium price of the long-term asset. Investors with more complete theories do not necessarily earn higher returns than those with less complete ones, who can earn above the risk-free rate. We provide two necessary conditions for a trader to earn above the risk-free rate.

There is evidence that people do not fully take into account how other people's actions depend on these other people's information. This paper defines and applies a new equilibrium concept in games with private information, cursed equilibrium, which assumes that each player correctly predicts the distribution of other players' actions, but underestimates the degree to which these actions are correlated with other players' information. We apply the concept to common-values auctions, where cursed equilibrium captures the widely observed phenomenon of the winner's curse, and to bilateral trade, where cursedness predicts trade in adverse-selections settings for which conventional analysis predicts no trade. We also apply cursed equilibrium to voting and signalling models. We test a single-parameter variant of our model that embeds Bayesian Nash equilibrium as a special case and find that parameter values that correspond to cursedness fit a broad range of experimental datasets better than the parameter value that corresponds to Bayesian Nash equilibrium.

Banning affirmative action from college admissions cannot prevent an admissions office that cares about diversity from achieving it in ways other than explicitly considering race. We model college admissions where candidates from two groups with different average qualiÞcations compete for a Þxed number of seats. Under affirmative action, an admissions office that cares both about quality and diversity admits the best-qualiÞed candidates from each group. Under a ban, it may promote diversity by partially ignoring candidates’ qualiÞcations and therefore not admitting the best-qualiÞed candidates from either group. A ban always reduces diversity and may also lower quality.

Most of the political economy literature blames inefficient policies on institutions or politicians’ motives to supply bad policy, but voters may themselves be partially responsible by demanding bad policy. In this article, we posit that voters may systematically err when assessing potential changes in policy by underappreciating how new policies lead to new equilibrium behaviour. This biases voters towards policy changes that create direct benefits—welfare would rise if behaviour were held constant—even if those reforms ultimately reduce welfare because people adjust behaviour. Conversely, voters are biased against policies that impose direct costs even if they induce larger indirect benefits. Using a lab experiment, we find that a majority of subjects vote against policies that, while inflicting direct costs, would help them to overcome social dilemmas and thereby increase welfare. Subjects also support policies that, while producing direct benefits, create social dilemmas and ultimately hurt welfare. Both mistakes arise because subjects fail to fully anticipate the equilibrium effects of new policies. More precisely, we establish that subjects systematically underappreciate the extent to which policy changes will affect the behaviour of other people, and that these mistaken beliefs exert a causal effect on the demand for bad policy.

We model a financial market where some traders of a risky asset do not fully appreciate what prices convey about others' private information. Markets comprising solely such “cursed” traders generate more trade than those comprising solely rationals. Because rationals arbitrage away distortions caused by cursed traders, mixed markets can generate even more trade. Per‐trader volume in cursed markets increases with market size; volume may instead disappear when traders infer others' information from prices, even when they dismiss it as noisier than their own. Making private information public raises rational and “dismissive” volume, but reduces cursed volume given moderate noninformational trading motives.