Modelling change in individual characteristics: an axiomatic framework

Economic models describe individuals in terms of underlying characteristics, such as taste for some good, sympathy level for another player, time discount rate, risk attitude, and so on. In real life, such characteristics change through experiences: taste for Mozart changes through listening to it, sympathy for another player through observing his moves, and so on. Models typically ignore change, not just for simplicity but also because it is unclear how to incorporate change. I introduce a general axiomatic framework for defining, analysing and comparing rival models of change. I show that seemingly basic postulates on modelling change together have strong implications, like irrelevance of the order in which someone has his experiences and ‘linearity’ of change. This is a step towards placing the modelling of change on solid axiomatic grounds and enabling non-arbitrary incorporation of change into economic models

Judgment aggregation in general logics

Within social choice theory, the new field of judgment aggregation aims to merge many individual sets of judgments on logically interconnected propositions into a single collective set of judgments on these propositions. Commonly, judgment aggregation is studied using standard propositional logic, with a limited expressive power and a problematic representation of conditional statements ('if P then Q') as material conditionals. In this methodological paper, I present a generalised model, in which most realistic decision problems can be represented. The model is not restricted to a particular logic but is open to several logics, including standard propositional logic, predicate calculi, modal logics and conditional logics. To illustrate the model, I prove an impossibility theorem, which generalises earlier results.judgement aggregation, discursive dilemma, modelling methodology, formal logics, impossibility theorem

Aggregation and the relevance of some issues for others

A general collective decision problem is analysed. It consists in many issues that are interconnected in two ways: by mutual constraints and by connections of relevance. The goal is to decide on the issues by respecting the mutual constraints and by aggregating in accordance with an informational constraint given by the relevance connections. Whether this is possible in a non-degenerate way depends on both types of connections and their interplay. One result, if applied to the preference aggregation problem and adopting Arrow''s notion of (ir)relevance, gives Arrow''s Theorem, without excluding indifferences unlike in the existing general aggregation literature.mathematical economics;

Aggregation theory and the relevance of some issues to others

I propose a general collective decision problem consisting in many issues that are interconnected in two ways: by mutual constraints and by connections of relevance. Aggregate decisions should respect the mutual constraints, and be based on relevant information only. This general informational constraint has many special cases, including premise-basedness and Arrow''s independence condition; they result from special notions of relevance. The existence and nature of (non-degenerate) aggregation rules depends on both types of connections. One result, if applied to the preference aggregation problem and adopting Arrow''s notion of (ir)relevance, becomes Arrow''s Theorem, without excluding indifferences unlike in earlier generalisations.mathematical economics;

Terrorism Prevention: A General Model

In this paper, I present and discuss a method for modelling an important trade-off faced by terrorism prevention policies: the trade-off between, on the one hand, trying to reduce people's inclination towards terrorism, and, on the other hand, trying to protect society against existing terrorists. In general, cause-related policies reduce inclination towards terrorism (first goal), involving measures such as raising the standard of living, and symptom-related policies reduce the power of terrorists (second goal), involving measures such as capturing and detaining terrorists. But, crucially, symptom-related policies also affect the inclination towards terrorism, through (desirable) deterrence and (undesirable) 'hate effects'. If 'hate effects' dominate over deterrence, more toughness overall increases inclination, possibly overcompensating the 'capture success'. So, symptom-related policies may face a trade-off between capturing terrorists, and thereby possibly creating new terrorists. Through the modelling method presented, both policy goals are simultaneously taken into account.terrorism, threat, war, symptom-related policy, cause-related policy, development policy, development aid, deterrence, hate effect, trade-off, game theory

Bayesian Group Belief

If a group is modelled as a single Bayesian agent, what should its beliefs be? I propose an axiomatic model that connects group beliefs to beliefs of group members, who are themselves modelled as Bayesian agents, possibly with different priors and different information. Group beliefs are proven to take a simple multiplicative form if people''s information is independent, and a more complex form if information overlaps arbitrarily. This shows that group beliefs can incorporate all information spread over the individuals without the individuals having to communicate their (possibly complex and hard-to-describe) private information; communicating prior and posterior beliefs suffices.mathematical economics;

Welfarism, Preferencism, Judgmentism

In a single framework, I address the question of the informational basis for evaluating social states. I particularly focus on information about individual welfare, individual preferences and individual (moral) judgments, but the model is also open to any other informational input deemed relevant, e.g. sources of welfare and motivations behind preferences. In addition to proving some possibility and impossibility results, I discuss objections against using information about only one aspect (e.g. using only preference information). These objections suggest a multi-aspect informational basis for aggregation. However, the multi-aspect approach faces an impossibility result created by a lack of inter-aspect comparability. The impossibility could be overcome by measuring information on non-cardinal scales.public economics ;

The possibility of judgment aggregation for network agendas

Within social choice theory, the new field of judgment aggregation aims at reaching collective judgments on a set of logically interconnected propositions. I investigate decision problems, in which the agenda is a network, composed of atomic propositions and connection rules between them. Networks can represent various realistic decision problems, including most concrete examples given in the literature. Nevertheless, networks are unexplored so far due to problems when modelling connection rules in standard propositional logic. By extending the logic, I prove that, for any network, decision rules satisfying the common conditions always exist, in contrast to the literature's emphasis on impossibilities. I also characterise the class of such decision rules, and propose a simple way to select a decision rule.judgment aggregation, collective inconsistency, possibility theorems, network, connection rule, formal logic, material conditional, subjunctive conditional