Tomas Sjöström

Is Grameen Lending Efficient? Repayment Incentives and Insurance in Village Economies

Many believe that a key innovation by the Grameen Bank is to encourage borrowers to help each other in hard times. To analyse this, we study a mechanism design problem where borrowers share information about each other, but their limited side contracting ability prevents them from writing complete insurance contracts. We derive a lending mechanism which efficiently induces mutual insurance. It is necessary for borrowers to submit reports about each other to achieve efficiency. Such cross-reporting increases the bargaining power of unsuccessful borrowers, and is robust to collusion against the bank. Copyright 2004, Wiley-Blackwell.

Arms Races and Negotiations

A state which does not desire an arms race may nevertheless acquire new weapons if it believes another state will acquire them. If each state assigns some arbitrarily small probability to the event that the other state has a dominant strategy to acquire more weapons, then a multiplier effect appears, and the unique Bayesian Nash equilibrium involves an arms race with probability one. However, if the prior probability that a player is a dominant strategy type is sufficiently small, then there is an equilibrium of the cheap-talk extension of the arms race game where the probability of an arms race is close to zero.

Intuition and Deliberation : Two Systems for Strategizing in the Brain

Optimal gaming requires matching the type of neural circuitry (intuitive versus deliberative) to the type of game. Playing More Games The neural mechanisms underlying strategic decision-making and social preferences can be teased apart by experimental “games.” In one class of two-player games known as dominance solvable, a unique strategy emerges that is the optimal one to adopt because it cannot be overcome by what the other player does. In a second class of games, there is no unique solution, and the optimal strategy requires the players to coordinate, which, in the absence of explicit communication, arises from a “meeting of minds.” Kuo et al. (p. 519) have conducted a neuroimaging study of subjects playing these two kinds of games and found that brain regions previously associated with deliberate and effortful reasoning are activated during dominance-solvable games, whereas other brain regions linked to social processing take the lead during coordination game playing. Dual-process theories distinguish between intuition (fast and emotional) and reasoning (slow and controlled) as a basis for human decision-making. We contrast dominance-solvable games, which can be solved by step-by-step deliberative reasoning, with pure coordination games, which must be solved intuitively. Using functional magnetic resonance imaging, we found that the middle frontal gyrus, the inferior parietal lobule, and the precuneus were more active in dominance-solvable games than in coordination games. The insula and anterior cingulate cortex showed the opposite pattern. Moreover, precuneus activity correlates positively with how “effortful” a dominance-solvable game is, whereas insula activity correlates positively with how “effortless” a coordination game is.

Entrepreneurial talent, occupational choice, and trickle up policies

We study market inefficiencies and policy remedies when agents choose their occupations, and entrepreneurial talent is subject to private information. Untalented entrepreneurs depress the returns to entrepreneurship because of adverse selection. The severity of this problem depends on the outside option of entrepreneurs, which is working for wages. This links credit, product and labor markets. A rise in wages reduces the adverse selection problem. These multimarket interactions amplify productivity shocks and may generate multiple equilibria. If it is impossible to screen entrepreneurs then all agents unanimously support a tax on entrepreneurs that drives out the less talented ones. However, if screening is possible, e.g., if wealthy entrepreneurs can provide collateral for their loans, then wealthy entrepreneurs do not support surplus enhancing taxes.

ON THE CONVERGENCE OF FICTITIOUS PLAY

We study the continuous time Brown-Robinson fictitious play process f or non-zero sum games. We show that, in general, fictitious play cannot converg e cyclically to a mixed strategy equilibrium in which both players use more tha n two pure strategies.

Secure Implementation Experiments:Do Strategy-proof Mechanisms Really Work?

Strategy-proofness, requiring that truth-telling is a dominant strategy, is a standard concept used in social choice theory. Saijo et al. (2003) argue that this concept has serious drawbacks. In particular, announcing ones true preference may not be a unique dominant strategy, and almost all strategy-proof mechanisms have a continuum of Nash equilibria. For only a subset of strategy-proof mechanisms do the set of Nash equilibria and the set of dominant strategy equilibria coincide. For example, this double coincidence occurs in the Groves mechanism when preferences are single-peaked. We report experiments using two strategy-proof mechanisms where one of them has a large number of Nash equilibria, but the other has a unique Nash equilibrium. We found clear differences in the rate of dominant strategy play between the two.

Bringing GATT into the Core

This paper calculates international income transfers which implement a Pareto optimal trade equilibrium in a world where many countries trade many goods.

Chapter 5 Implementation theory

Abstract The implementation problem is the problem of designing a mechanism (game form) such that the equilibrium outcomes satisfy a criterion of social optimality embodied in a social choice rule. If a mechanism has the property that, in each possible state of the world, the set of equilibrium outcomes equals the set of optimal outcomes identified by the social choice rule, then the social choice rule is said to be implemented by this mechanism. Whether or not a social choice rule is implementable may depend on which game-theoretic solution concept is used. The most demanding requirement is that each agent should always have a dominant strategy, but mainly negative results are obtained in this case. More positive results are obtained using less demanding solution concepts such as Nash equilibrium. Any Nash-implementable social choice rule must satisfy a condition of “monotonicity”. Conversely, any social choice rule which satisfies monotonicity and “no veto power” can be Nash-implemented. Even non-monotonic social choice rules can be implemented using Nash equilibrium refinements. The implementation problem can be made more challenging by imposing additional requirements on the mechanisms, such as robustness to renegotiation and collusion. If the agents are incompletely informed about the state of the world, then the concept of Nash equilibrium is replaced by Bayesian Nash equilibrium. Incentive compatibility is a necessary condition for Bayesian Nash implementation, but in other respects the results closely mimic those that obtain with complete information.

Competition and the evolution of efficiency

Abstract This paper presents an evolutionary model of the relationship between inter-firm competition and intra-firm organizational or X-efficiency. We model X-inefficiency within the firm as a prisoners dilemma effort-monitoring problem, whose evolution is influenced by external competitive pressure from other firms. A closed form stochastic equilibrium displaying “survival of the fittest” dynastic cycles is derived and analyzed. The main result is that there exists a well defined sense in which competition is a surprisingly powerful force for efficiency.

Local public goods, debt and migration

Migration raises a potential free rider problem for the provision of durable local public goods if the late-comers can enjoy the public good without paying for it. Allowing communities to finance public goods by debt mitigates this problem, since future immigrants have to share the burden of the debt. However, in equilibrium there will be over-accumulation of local debt. There may be more or less public good than in first best, but conditional on the inefficiently high levels of debt there will be too few public goods. A competitive market for land reduces but does not in general eliminate the inefficiencies.