Friendship Selection

We model the formation of friendships as repeated cooperation within a set of heterogeneous players. The model builds around three of the most important facts about friendship: friends help each other, there is reciprocity in the relationship and people usually have few friends. In our results we explain how similarity between people affects the friendship selection. We also characterize when the friendship network won’t depend on the random process by which people meet each other. Finally, we explore how players’ patience influences the length of their friendship relations. Our results match and explain empirical evidence reported in social studies on friendship. For instance, our model explains why troublesome subjects have few friends.Friendship, cooperative game, grim trigger strategy, social networks

Probability Matching and Reinforcement Learning*

Probability matching occurs when an action is chosen with a frequency equivalent to the probability of that action being the best choice. This sub-optimal behavior has been reported repeatedly by psychologist and experimental economist. We provide an evolutionary foundation for this phenomenon by showing that learning by reinforcement can lead to probability matching and, if learning occurs suffciently slowly, probability matching does not only occur in choice frequencies but also in choice probabilities. Our results are completed by proving that there exists no quasi-linear reinforcement learning specification such that behavior is optimal for all environments where counterfactuals are observed.Probability Matching; Reinforcement Learning

Cooperation, Imitation and Correlated Matching

We study a setting where imitative players are matched into pairs to play a Prisoners' Dilemma game. A well know result in such setting is that under random matching cooperation vanishes for any interior initial condition. The novelty of this paper is that we add a certain correlation to the matching process: players that belong to a pair were both parties cooperate repeat partner next period whilst all other players are randomly matched into pairs. This intuitive correlation introduced in the matching process makes cooperation the unique outcome in the long run under some conditions. Furthermore, we show that no assortative equilibrium exits.Cooperation; Correlated Matching; Imitation; Prisoners' Dilemma

Learn Without Counterfactuals

In this paper we study learning procedures when counterfactuals (payo s of not-chosen actions) are not observed. The decision maker reasons in two steps: First, she updates her propensities for each action after every payo experience, where propensity is de ned as how much she prefers each action. Then, she transforms these propensities into choice probabilities. We introduce natural axioms in the way propensities are updated and the way propensities are translated into choice, and study the decision marker's behavior when such axioms are in place.Adaptive Learning; Counterfactuals; Partial Information; Reinforcement Learning

Cash Incentives and Unhealthy Food Consumption

The costs associated with unhealthy food consumption are not only paid by those suffering from overweight but by all members of society in terms of higher costs for social security systems. With this in mind, we study the effectiveness of a tax, a subsidy and cash incentives in reducing unhealthy food consumption. Using an inter-temporal rational choice model with habit, we calibrate and simulate the effect of those policies to US and UK data.  Our findings suggest that cash incentives may be the most effective policy in reducing unhealthy food consumption yet it can be the most costly one. Taxes are relatively ineffective in reducing unhealthy food consumption. Subsidies have the best balance between effectiveness and monetary benefits to the society.    Habit; Junk Food; Overweight; Public Policy; Rational Addiction

Learning within a Markovian Environment

We investigate learning in a setting where each period a population has to choose between two actions and the payoff of each action is unknown by the players. The population learns according to reinforcement and the environment is non-stationary, meaning that there is correlation between the payoff of each action today and the payoff of each action in the past. We show that when players observe realized and foregone payoffs, a suboptimal mixed strategy is selected. On the other hand, when players only observe realized payoffs, a unique action, which is optimal if actions perform different enough, is selected in the long run. When looking for efficient reinforcement learning rules, we find that it is optimal to disregard the information from foregone payoffs and to learn as if only realized payoffs were observed.Adaptive Learning, Markov Chains, Non-stationarity, Reinforcement Learning

Cooperation in Repeated Games, Bounded Rational Learning and the Adoption of Evolving Technologies.

No abstract availableGame theory; Decision making;

Bioinformática aplicada a biología integrativa y de sistemas en cáncer

Máster Universitario en Biología y Clínica del Cáncer: Programa, Objetivos y Metodología.Peer Reviewe

Espais d'Acció i Aventura

El present article pretén explicar una de les pràctiques educatives que es porten a terme al Col·legi d'Educació Infantil i Primària Pío XII d'Osca. Als seus inicis, els espais d'acció i aventura van ser una experiència docent encaminada a què els nens petits poguessin satisfer la seva necessitat de joc i moviment en el propi centre escolar. Avui dia s'han convertit en una proposta didàctica, concreta i sistemàtica, basada en la manipulació pedagògica de la circumstància ambiental, que pot orientar la realització d'una activitat física natural en l'educació del nen de 3 a 8 anys. Als espais d'acció i aventura, cada nen, en funció de les seves característiques personals, pot trobar la situació ambiental adient per a manifestar les seves capacitats i marcar-se un ritme d'avançament progressiu en el seu desenvolupament. A més, els espais d'acció i aventura constitueixen un marc peculiar que afavoreix l'aparició d'una dinàmica d'interacció especialment rica entre els nens i entre aquests i l'adult. Aquesta dinàmica d'interacció impulsa les potencialitats dels petits i possibilita que posin en marxa diversos comportaments que els condueixen a un desenvolupament òptim i equilibrat de la seva personalitat

Espacios de Acción y Aventura

El presente artículo pretende explicar una de las prácticas educativas que se llevan a cabo en el Colegio de Educación Infantil y Primaria Pío XII de Huesca. En sus inicios, los espacios de acción y aventura fueron una experiencia docente encaminada a que los niños pequeños pudieran satisfacer su necesidad de juego y movimiento en el propio centro escolar. Hoy día se han convertido en una propuesta didáctica, concreta y sistemática, basada en la manipulación pedagógica de la circunstancia ambiental, que puede orientar la realización de una actividad física natural en la educación del niño de 3 a 8 años. En los espacios de acción y aventura, cada niño, en función de sus características personales, puede encontrar la situación ambiental adecuada para manifestar sus capacidades y marcarse un ritmo de avance progresivo en su desenvolvimiento. Además, los espacios de acción y aventura constituyen un marco peculiar que favorece la aparición de una dinámica de interacción especialmente rica entre los niños y entre éstos y el adulto. Esta dinámica de interacción impulsa las potencialidades de los pequeños y posibilita que pongan en marcha diversos comportamientos que les conducen a un desarrollo óptimo y equilibrado de su personalidad