Willemien Kets

MEDS, Kellogg School of Management

Phone: +1 (505) 204-8012
Email: w-kets@kellogg.northwestern.edu

Curriculum Vitae


A belief-based theory of homophily (with Alvaro Sandroni)

Homophily, the tendency to interact with similar people, is a well-documented phenomenon that has important economic implications. We provide a belief-based explanation of homophily. Building on the dual process account of Theory of Mind in psychology, we assume that players with a similar background have similar impulses telling them which action is appropriate. Players are introspective and recognize that their own impulses are a good predictor of the impulses of players that are like them, and realize that others are likewise introspective. We show that if players can sort (e.g., by choosing certain occupations) to meet people like them, then high levels of homophily are possible even with limited asymmetries in preferences. Intuitively, the introspective process amplifies small asymmetries in preferences, allowing for effective coordination.

Finite Depth of Reasoning and Equilibrium Play in Games with Incomplete Information (submitted).
Online appendix.

If players have a finite depth of reasoning, can their equilibrium behavior be described by the standard framework? Intuitively, one might expect that “simple” Harsanyi type spaces, in which the beliefs of types are determined by the first few orders of beliefs, would be good “as-if models” models for finite-depth type spaces. However, I show that this is not the case: for any finite-depth type space, there is no Harsanyi type space (simple or not simple) that gives the same equilibrium behavior in all games.

Robust Multiplicity with a Grain of Naiveté (with Aviad Heifetz; submitted).
Online appendix.

In global games and other games with sufficiently rich payoffs, types typically have a unique rationalizable action (Weinstein & Yildiz, '07). This result, however, presumes that players have an infinite depth of reasoning and that this is common belief. We show that multiplicity of rationalizable outcomes is a typical and robust phenomenon if we relax that assumption only slightly, i.e., if players have an infinite depth and this is almost common belief.

Ranking Friends (with Yossi Feinberg; submitted).

Say you need a friend to help you move. You call your friends one by one to see whether one of them can help. If a friend does not or cannot help you (for example, because she can't get the day off, or because she doesn't even try), you call the next friend on your list. If everyone has such a list, or ranking, of friends, and needs help on a regular basis, what is the optimal social structure?

Ambiguous Language and Consensus (with Joe Halpern; submitted).

Language, and communication more generally, is often ambiguous, i.e., can be interpreted in different ways. In a series of papers, we develop a logic to model this, and investigate its consequences for belief formation and consensus. In one application, we show that in the presence of ambiguity, the claim of Aumann (1987) that ``there is no rational basis for people who have always been fed precisely the same information to [entertain different probabilities]'' holds only under very restrictive assumptions: players' beliefs can be consistent with a common prior only if all information is public, not just common, that is, all players receive the same signals, and this is common belief.


Robustness of equilibria in anonymous local games, Journal of Economic Theory, 146, pp. 300–325, 2011.
Online appendix.
(Working paper version.)

Inequality and network structure (with Garud Iyengar, Rajiv Sethi and Sam Bowles), Games and Economic Behavior 73, pp. 215–226, 2011.
(Working paper version.)

Learning to be prepared (with Mark Voorneveld), International Journal of Game Theory 37, pp. 333–352, 2008.
(Working paper version.)

An axiomatization of minimal curb sets (with Mark Voorneveld and Henk Norde), International Journal of Game Theory 33, pp. 479–490, 2005.
(Working paper version.)

Publications in Other Fields

Betting Strategies, Market Selection, and the Wisdom of Crowds (with David Pennock, Rajiv Sethi and Nisarg Shah); Twenty-Eighth AAAI Conference on Artificial Intelligence (AAAI-14), 2014; forthcoming.

A logic for reasoning about ambiguity (with Joe Halpern); Artificial Intelligence, 2014; forthcoming.

Ambiguous language and differences in beliefs. Proceedings of KR2012, 2012. Ray Reiter Best Paper Award.

Random intersection graphs with a tunable degree distribution and clustering (with Mia Deijfen), Probability in the Engineering and Informational Sciences 23, pp. 661–674, 2008.

Zn- and Cd-induced features at the GaAs(110) and InP(110) surfaces studied by low-temperature scanning tunneling microscopy (with Randy de Kort, Maurice van der Wielen, Ari van Roij, and Herman van Kempen), Physical Review B 63, 125336, 2001.

A low-temperature scanning tunneling microscopy study on the Sn- and Zn-doped InP(110) surfaces (with Randy de Kort and Herman van Kempen), Surface Science 482, pp. 495–500, 2001.

Peer-Reviewed Surveys

Learning with fixed rules: The minority game, Journal of Economic Surveys. Forthcoming.

Free trade and its enemies (with Paul Tang), De Economist, pp. 152–153, pp. 427–437, 2004.