Learnability and rationality of choice

In this paper we study the learnability of the class of rationalizable choice functions using the basic concept of PAC-learnability from statistical learning theory. We prove that the class of rationalizable choice functions on N alternatives is learnable from O(N) examples and is optimal in terms of PAC-learnability among classes which are invariant under permutations of the elements.     

An Afriat Theorem for the collective model of household consumption

We provide a nonparametric ‘revealed preference’ characterization of rational household behavior in terms of the collective consumption model, while accounting for general individual preferences that can be non-convex. Our main result is the Collective Afriat Theorem, which parallels the well-known Afriat Theorem for the unitary model. First, it provides a characterization of collectively rational consumption behavior in terms of collective Afriat inequalities. Next, it implies the Collective Axiom of Revealed Preference (CARP) as a testable necessary and sufficient condition for data consistency with collective rationality. Finally, the theorem has some interesting testability implications. With only a finite set of observations, the nature of consumption externalities (positive or negative) in the intra-household allocation process is non-testable. The same non-testability conclusion holds for privateness (with or without externalities) or publicness of consumption. By contrast, concavity of individual utility functions (representing convex preferences) turns out to be testable. In addition, monotonicity is testable for the model that assumes all household consumption is public.     

Reputation, group structure and social tensions

Social tensions impede social cohesion and public goods provision, and can be a driving force for more serious conflicts such as civil wars. Surprisingly, the emergence of social tensions has been studied only rarely in the literature. In the present contribution a game-theoretic model highlights how reputation concerns and the structure of group cleavages matter for the emergence of social tensions. In particular, the respective effects of ethnic fractionalization, polarization and segregation are analyzed. The differences between ethnicity and class, and the role of social mobility are also studied. The predictions of the model can account for recent empirical evidence.     

Imitation and the evolution of Walrasian behavior: Theoretically fragile but behaviorally robust

A well-known result by Vega-Redondo (1997) [18] implies that in symmetric Cournot oligopolies, imitation leads to the Walrasian outcome. We show that this result is not robust to the slightest asymmetry in costs, since every outcome where agents choose identical actions will be played some fraction of the time in the long run. We then conduct experiments to check this fragility. We obtain that, contrary to the theoretical prediction, the Walrasian outcome is a good predictor of market outcomes. Finally, we suggest a new theory based on a mix of imitation and other learning processes that explains subjects' behavior fairly well.     

Natural capital, subjective well-being, and the new welfare economics of sustainability: Some evidence from cross-country regressions

The measurement of natural capital and its management during the economic development process are important aspects of the capital approach to sustainable development. However, the assessment of social welfare in terms of genuine savings (or changes in total wealth per capita) is arguably too limited. This paper tries to make a case for the incorporation of subjective well-being measures in debates about sustainable development by exploring the macro-level relationship between subjective well-being and natural capital in a cross-country setting. It is tested whether natural capital per capita is correlated with subjective well-being in a sample of fifty-eight developed and developing countries, using natural capital data from the World Bank's Millennium Capital Assessment. Bivariate regressions indicate that it is. When multiple regression models are estimated that include (a) major country-level determinants of subjective well-being (GNI per capita, social capital, income distribution, unemployment, inflation), and (b) regional dummy variables for ex-Soviet Union and Latin American countries, the positive correlation remains. The role of data outliers is carefully explored, and the sensitivity of the results to the use of alternative subjective well-being measures (i.e. life satisfaction, happiness, and a combined life satisfaction and happiness index) is investigated. This does not change the nature of the results. The findings arguably strengthen the case for a ‘new welfare economics of sustainability’ that takes subjective well-being measures into account.     

Spatial dynamics and convergence: The spatial AK model

We study the optimal dynamics of an AK economy where population is uniformly distributed along the unit circle. Locations only differ in initial capital endowments. Spatio-temporal capital dynamics are described by a parabolic partial differential equation. The application of the maximum principle leads to necessary but non-sufficient first-order conditions. Thanks to the linearity of the production technology and the special spatial setting considered, the value function of the problem is found explicitly, and the (unique) optimal control is identified in feedback form. Despite constant returns to capital, we prove that the spatio-temporal dynamics, induced by the willingness of the planner to give the same (detrended) consumption over space and time, lead to convergence in the level of capital across locations in the long-run.     

Tail return analysis of Bear Stearns' credit default swaps

We compare several models for Bear Stearns' credit default swap spreads estimated via a Markov chain Monte Carlo algorithm. The Bayes Factor selects a CKLS model with GARCH–EPD errors as the best model. This model best captures the volatility clustering and extreme tail returns of the swaps during the crisis. Prior to November 2007, only four months ahead of Bear Stearns' collapse though, the swap spreads were indistinguishable statistically from the risk-free rate.     

Invariance of conditional maximum utility

The consumer benefit in a discrete choice model is often measured by maximum utility. We characterize the conditional (on the chosen alternative) and the unconditional distribution of maximum utility. We show that among a wide class of distributions (independent with convex supports) of error terms, the Type I extreme-value distribution is the unique distribution which ensures that all the conditional distributions of maximum utility coincide. Moreover, we show that for i.i.d. (with convex support) error terms, the invariance of conditional expected maximum utility characterizes the multinomial logit model.     

DUOPOLY IN THE JAPANESE AIRLINE MARKET: BAYESIAN ESTIMATION FOR THE ENTRY GAME*

This paper provides an econometric analysis of a duopoly game in the Japanese domestic airline market. We establish a novel Bayesian estimation approach for the entry game, which allows the incorporation of flexible inference techniques. We find asymmetric strategic interactions between Japanese firms. This result implies that competition is still influenced by the former regulation regime. Furthermore, our prediction analysis indicates that the new Shizuoka airport will suffer from a lack of demand in the future.     

International portfolio reallocation: Diversification benefits and European monetary union

We investigate the determinants of bilateral international equity and bond portfolio reallocation across a large cross-section of countries spanning over two sample periods: 1997-2001 and 1997-2005. We find that the strongest drivers are the marginal diversification benefits arising from the pure asset component and the initial degree of underweight. This evidence suggests that global portfolio reallocations over the asset boom and bust period were determined by optimal diversification considerations. We also find that due to economic and monetary union (EMU) the weight assigned by euro area investors to investment in euro area countries increased significantly in equity and fixed income portfolios, with a trade diverting effect against the British bond market.     

Controlling portfolio skewness and kurtosis without directly optimizing third and fourth moments

In spite of their importance, third or higher moments of portfolio returns are often neglected in portfolio construction problems due to the computational difficulties associated with them. In this paper, we propose a new robust mean–variance approach that can control portfolio skewness and kurtosis without imposing higher moment terms. The key idea is that, if the uncertainty sets are properly constructed, robust portfolios based on the worst-case approach within the mean–variance setting favor skewness and penalize kurtosis.     

A new estimator for trade costs and its small sample properties

This paper discusses the estimation of parameters of a traditional transportation model, as it is typically present in so-called Takayama–Judge type spatial price equilibrium models. In contrast to previously used estimation methods, observations of regional prices as well as of trade costs are used in a direct estimation of the first order conditions. The proposed method uses bi-level programming techniques to minimize a weighted least squares criterion under the restriction that the estimated parameters satisfy the Kuhn–Tucker conditions for an optimal solution of the transport model. A penalty function and a smooth reformulation are used to iteratively approximate the complementary slackness conditions. Monte-Carlo simulations are used to trace out some properties of the estimator and compare it with a traditional calibration method. The analysis shows that the proposed technique estimates prices as well as trade costs more precisely than the traditional calibration method. It is suggested to apply the same method to a range of linear and quadratic models.     

On the relation between regular variation and the asymptotic elasticity of substitution

This paper characterizes a class of regularly varying production functions with an asymptotic elasticity of substitution equal to one. In particular, it is shown that these functions asymptotically approximate the Cobb–Douglas form. The results generalize and unify existing results in the literature.     

Estimating VARs with long stationary heterogeneous panels: A comparison of the fixed effect and the mean group estimators

The most promising candidates for estimating vector autoregressive models with long, stationary, possibly heterogeneous panel data sets (panel-VARs) are the fixed effect (FE) and the mean group (MG) estimators. With a view to providing guidance to applied researchers on how to pool in a panel-VAR, this paper compares the performance of the FE and the MG estimators both asymptotically and in Monte Carlo simulations. The main results of the analysis suggest the use of both estimators in applied work. If FE and MG estimates give similar estimates, the FE estimator should be used because it is more efficient. If they differ, the MG estimator should be used only if the panel is sufficiently long — say, twice as long as usually recommended in the dynamic panel data literature. If FE and MG estimates differ and the panel is not long enough, neither is generally a desirable alternative and other estimation techniques are needed.     

Regulation and pricing of pharmaceuticals: Reference pricing or price cap regulation?

We study the relationship between regulatory regimes and pharmaceutical firms’ pricing strategies using a unique policy experiment in Norway, which in 2003 introduced a reference price (RP) system called “index pricing” for a sub-sample of off-patent pharmaceuticals, replacing the existing price cap (PC) regulation. We estimate the effect of the reform using a product level panel dataset, covering the drugs exposed to RP and a large number of drugs still under PC regulation in the time before and after the policy change. Our results show that RP significantly reduces both brand-name and generic prices within the reference group, with the effect being stronger for brand-names. We also identify a negative cross-price effect on therapeutic substitutes not included in the RP system. In terms of policy implications, the results suggest that RP is more effective than PC regulation in lowering drug prices, while the cross-price effect raises a concern about patent protection.     

The dynamics of a differentiated duopoly with quantity competition

We analyse the dynamics of a Cournot duopoly with heterogeneous players to investigate the effects of micro-founded differentiated products demand on stability. The present study, which indeed modifies and extends Zhang et al. (2007) (Zhang, J., Da, Q., Wang, Y., 2007. Analysis of nonlinear duopoly game with heterogeneous players. Economic Modelling 24, 138–148) and Tramontana, F., (2010) (Tramontana, F., 2010. Heterogeneous duopoly with isoelastic demand function. Economic Modelling 27, 350–357), reveals that a higher degree of product differentiation may destabilise the market equilibrium. Moreover, we show that a cascade of flip bifurcations may lead to periodic cycles and ultimately chaotic behaviours. Since a higher degree of product differentiation implies weaker competition, then a theoretical implication of our findings, that also constitute a policy warning, is that a fiercer (weaker) competition tends to stabilise (destabilise) the unique positive Cournot–Nash equilibrium.     

The Cournot-Bertrand model and the degree of product differentiation

We consider a duopoly model with a Cournot-type firm and a Bertrand-type firm. Both survive and the equilibrium is stable when there is sufficient product differentiation. With no differentiation, only the Cournot-type firm survives, and the outcome is perfectly competitive.