Measuring relative non-motorized accessibility to retail activities

Accessibility planning is a crucial alternative to mobility planning for reaching sustainable outcomes. Although there is a vast literature on accessibility, less attention is paid to accessibility as a relative concept, i.e., its relationship with the socio-economic characteristic of the population. While accessibility is known to vary by location, it also changes as a consequence of differences in individual willingness to reach destinations by certain transport modes. Using the city of Zaragoza, Spain as a case study, this paper evaluates relative non-motorized accessibility (walking and cycling) to three types of retail activities: daily, weekly, and incidental. First, a clustering process is used to identify four population groups according to their socio-economic characteristics (the young employed; the young unemployed; seniors and adults). Second, distance-decay functions based on time-willingness to reach retail destinations by non-motorized modes are compared between the four clusters of population. Third, relative accessibility maps based on gravity-based models are elaborated, highlighting places that exhibit statistical differences between the population clusters. The results indicate that willingness to reach retail stores on foot by seniors (>65?years old) was significantly different from the rest of groups analyzed, providing additional insights on how relative accessibility measurements can anticipate potential social exclusion risks.     

Unawareness and bankruptcy: A general equilibrium model

Summary. We present a consistent pure-exchange general equilibrium model where agents may not be able to foresee all possible future contingencies. In this context, even with nominal assets and complete asset markets, an equilibrium may not exist without appropriate assumptions. Specific examples are provided. An existence result is proved under the main assumption that there are sufficiently many states that all the agents foresee. An intrinsic feature of the model is bankruptcy, which agents may involuntarily experience in the unforeseen states. Received: April 23, 1997; revised version: May 19, 1997     

Better Late than Early: Vertical Differentiation in the Adoption of a New Technology

After the initial breakthrough in the research phase of R&D, a new product undergoes a process of change, improvement, and adaptation to market conditions. We model the strategic behavior of firms in this development phase. We emphasize that a key dimension to this competition is the innovation that leads to product differentiation and quality improvement. In a duopoly model with a single adoption choice, we derive endogenously the level and diversity of product innovations. We demonstrate the existence of equilibria in which one firm enters early with a low-quality product while the other continues to develop the technology and eventually markets a high-quality good. In such an equilibrium, no monopoly rent is dissipated and the later innovator makes more profits. Incumbent firms may well be the early innovators, contrary to the predictions of the "incumbency inertia" hypothesis.     

Dynamic variational preferences

We introduce and axiomatize dynamic variational preferences, the dynamic version of the variational preferences we axiomatized in [F. Maccheroni, M. Marinacci, A. Rustichini, Ambiguity aversion, robustness, and the variational representation of preferences, Mimeo, 2004], which generalize the multiple priors preferences of Gilboa and Schmeidler [Maxmin expected utility with a non-unique prior, J. Math. Econ. 18 (1989) 141-153], and include the Multiplier Preferences inspired by robust control and first used in macroeconomics by Hansen and Sargent (see [L.P. Hansen, T.J. Sargent, Robust control and model uncertainty, Amer. Econ. Rev. 91 (2001) 60-66]), as well as the classic Mean Variance Preferences of Markovitz and Tobin. We provide a condition that makes dynamic variational preferences time consistent, and their representation recursive. This gives them the analytical tractability needed in macroeconomic and financial applications. A corollary of our results is that Multiplier Preferences are time consistent, but Mean Variance Preferences are not.     

Optimal guessing: Choice in complex environments

In this paper, we extend the analysis of our earlier work on boundedly rational learning in an i.i.d. setting [Easley and Rustichini, Econometrica 67 (1999) 1157-1184] to complex decision problems. We show that the axioms from our earlier analysis can be applied in this more complex setting, and along with some new axioms, they asymptotically yield expected utility maximization. Perhaps most important is our demonstration of a simple procedure that insures expected payoff maximization no matter what Markov process the underlying process on states follows. We view this result as providing a positive learning result for all worlds in which learning is possible.     

Economies with observable types

We study economies of asymmetric information with observable types. Trade takes place in lotteries. Individuals face a standard budget constraint, while the incentive compatibility constraints are imposed on the production set of the intermediaries. This formalization encompasses moral hazard, as in [Jerez, 2003] and [Jerez, 2005], and private information economies. Equilibrium allocations are constrained efficient, but, contrary to what stated for example in Jerez (2005), the set of equilibrium allocations may be empty and the Second Welfare Theorem may fail. This happens for two reasons. First, constrained efficient allocations may violate the necessary and sufficient conditions of price supportability for the individuals. Second, even when constrained efficient allocation are price supportable, they may fail to be a profit maximizing choice of the firm at the individual supporting prices. To restore existence of an equilibrium the firm has to be restricted to supply allocations with support in the set of incentive compatible contracts.     

Demographic processes in a model of innovation diffusion with dynamic market

In this paper we study a binomial innovation diffusion model for a variable size market by modelling the demographic process of entrance-exit from each market compartment. We examine from a theoretical point of view the effect of the simultaneous presence of economic and demographic parameters under the exponential market growth hypothesis, by presenting some general results on the adoptions and sales time path. We also enlighten the relevance of considering these variables in relative terms and show how, in presence of a dynamic, the diffusion process never saturates the market. Finally, we test our model on a data set for cellular phones market in different countries.     

Equilibria in large games with continuous procedures

We study existence of equilibria in large games where players use boundedly rational procedures. The equilibria are different from Nash equilibria; the difference persists even when players use procedures for which the observations gathered in any period are used to evaluate the payoff from different actions.