Navin Kartik Publications

Signaling is wasteful. But how wasteful? We study the fraction of surplus dissipated in a separating equilibrium. For isoelastic environments, this waste ratio has a simple formula: β/(β + σ), where β is the benefit elasticity (reward to higher perception) and σ is the elasticity of higher types’ relative cost advantage. The ratio is constant across types and independent of other parameters, including convexity of cost in the signal. A constant waste ratio characterizes the isoelastic class. In winner-take-all signaling tournaments with N candidates, exactly (N − 1)/N of the surplus dissipates—the same as in Tullock contests.

We study two-player constant-sum Bayesian games with type-independent payoffs. Under a “completeness” statistical condition, any “identifiable” equilibrium is an ex-post equilibrium. We apply this result to a Downsian election in which office-motivated candidates possess private information about policy consequences. The ex-post property implies a sharp bound on information aggregation: equilibrium voter welfare is at best equal to the efficient use of a single candidate’s information. In canonical specifications, politicians may “anti-pander” (overreact to their information), whereas some degree of pandering would be socially beneficial. We discuss other applications of the ex-post result.

Does electoral replacement ensure that officeholders eventually act in voters’ interests? We study a reputational model of accountability. Voters observe incumbents’ performance and decide whether to replace them. Politicians may be “good” types who always exert effort or opportunists who may shirk. We find that good long-run outcomes are always attainable, though the mechanism and its robustness depend on economic conditions. In environments conducive to incentive provision, some equilibria feature sustained effort, yet others exhibit some long-run shirking. In the complementary case, opportunists are never fully disciplined, but selection dominates: every equilibrium eventually settles on a good politician, yielding permanent effort.

Many US colleges now use test-optional admissions. A frequent claim is that by not seeing standardized test scores, a college can admit a student body it prefers, say, with more diversity. But how can observing less information improve decisions? This paper proposes that test-optional policies are a response to social pressure on admission decisions. We model a college that bears disutility when it makes admission decisions that "society" dislikes. Going test optional allows the college to reduce its "disagreement cost." We analyze how missing scores are imputed and the consequences for the college, students, and society.

US colleges often justify test-optional admissions policies as promoting diversity by reducing their reliance on standardized test scores. But a college that mandates test scores can decide how to use those scores. Wouldn't more information allow a college to make decisions it prefers? Indeed, this paper identifies a broad set of assumptions under which test-mandatory policies are always weakly better for colleges. We then discuss how alternative assumptions might rationalize test-optional policies.

We study a model of signaling in which agents are heterogeneous on two dimensions. An agent’s natural action is the action taken in the absence of signaling concerns. Her gaming ability parameterizes the cost of increasing the action. Equilibrium behavior muddles information across dimensions. As incentives to take higher actions increase—due to higher stakes or more manipulable signaling technology—more information is revealed about gaming ability, and less about natural actions. We explore a new externality: showing agents’ actions to additional observers can worsen information for existing observers. Applications to credit scoring, school testing, and web searching are discussed.

We study observational learning in environments with congestion costs: an agent's payoff from choosing an action decreases as more predecessors choose that action. Herds cannot occur if congestion on every action can get so large that an agent prefers a different action regardless of his beliefs about the state. To the extent that switching away from the more popular action reveals private information, it improves learning. The absence of herding does not guarantee complete (asymptotic) learning, however, as information cascades can occur through perpetual but uninformative switching between actions. We provide conditions on congestion costs that guarantee complete learning and conditions that guarantee bounded learning. Learning can be virtually complete even if each agent has only an infinitesimal effect on congestion costs. We apply our results to markets where congestion costs arise through responsive pricing and to queuing problems where agents dislike waiting for service.

We study the characteristics of self-selected candidates in corrupt political systems. Individuals differ along two dimensions of unobservable character: public spirit (altruism) and honesty (disutility from selling out to special interests). Both aspects combine to determine an individual's quality as governor. We characterize properties of equilibrium candidate pools for arbitrary costs of running for office, including when costs become vanishingly small. We explore how policy instruments such as the governor's compensation and anticorruption enforcement affect the expected quality of governance through candidate self-selection. We show that self-selection can have surprising implications for the effect of information disclosures concerning candidates' backgrounds.

We consider full implementation in complete-information environments when agents have an arbitrarily small preference for honesty. We offer a condition called separable punishment and show that when it holds and there are at least two agents, any social choice function can be implemented by a simple mechanism in two rounds of iterated deletion of strictly dominated strategies.

An agent advises a principal on selecting one of multiple projects or an outside option. The agent is privately informed about the projects' benefits and shares the principal's preferences except for not internalizing her value from the outside option. We show that for moderate outside option values, strategic communication is characterized by pandering: the agent biases his recommendation toward “conditionally better-looking” projects, even when both parties would be better off with some other project. A project that has lower expected value can be conditionally better-looking. We develop comparative statics and implications of pandering. Pandering is also induced by an optimal mechanism without transfers

We generalize the canonical problem of Nash implementation by allowing agents to voluntarily provide discriminatory signals, i.e., evidence. Evidence can either take the form of hard information or, more generally, have differential but nonprohibitive costs in different states. In such environments, social choice functions that are not Maskin-monotonic can be implemented. We formulate a more general property, evidence monotonicity, and show that this is a necessary condition for implementation. Evidence monotonicity is also sufficient for implementation in economic environments. In some settings, such as when agents have small preferences for honesty, any social choice function is evidence-monotonic. Additional characterizations are obtained for hard evidence. We discuss the relationship between the implementation problem where evidence provision is voluntary and a hypothetical problem where evidence can be chosen by the planner as part of an extended outcome space.

This note shows that the conventional outcome associated with Bertrand competition with homogenous products and different marginal costs is obtained in every Nash equilibrium in which firms use undominated strategies. This strengthens an existence result due to Blume (2003).

This paper studies a simple model of observational learning where agents care not only about the information of others but also about their actions. We show that despite complex strategic considerations that arise from forward-looking incentives, herd behavior can arise in equilibrium. The model encompasses applications such as sequential elections, public good contributions, and leadership charitable giving.

I study a model of strategic communication between an uninformed Receiver and an informed but upwardly biased Sender. The Sender bears a cost of lying, or more broadly, of misrepresenting his private information. The main results show that inflated language naturally arises in this environment, where the Sender (almost) always claims to be of a higher type than he would with complete information. Regardless of the intensity of lying cost, there is incomplete separation, with some pooling on the highest messages. The degree of language inflation and how much information is revealed depend upon the intensity of lying cost. The analysis delivers a framework to span a class of cheap-talk and verifiable disclosure games, unifying the polar predictions they make under large conflicts of interest. I use the model to discuss how the degree of manipulability of information can affect the trade-off between delegation and communication.

We study costs and benefits of differences of opinion between an adviser and a decision maker. Even when they share the same underlying preferences over decisions, a difference of opinion about payoff‐relevant information leads to strategic information acquisition and transmission. A decision maker faces a fundamental trade‐off: a greater difference of opinion increases an adviser's incentives to acquire information but exacerbates the strategic disclosure of any information that is acquired. Nevertheless, when choosing from a rich pool of opinion types, it is optimal for a decision maker to select an adviser with some difference of opinion. Centralization of authority is essential to harness these incentive gains since delegation to the adviser can discourage effort.