A Characterization of single-peaked preferences

We identify in this paper two conditions that characterize the domain of single-peaked preferences on the line in the following sense: a preference profile satisfies these two properties if and only if there exists a linear order $L$ over the set of alternatives such that these preferences are single-peaked with respect L. The first property states that for any subset of alternatives the set of alternatives considered as the worst by all agents cannot contains more than 2 elements. The second property states that two agents cannot disagree on the relative ranking of two alternatives with respect to a third alternative but agree on the (relative) ranking of a fourth one. Classification-JEL: D71, C78

Scoring rules on dichotomous preferences

In this paper, we study individual incentives to report preferences truthfully for the special case when individuals have dichotomous preferences on the set of alternatives and preferences are aggregated in form of scoring rules. In particular, we show that (a) the Borda Count coincides with Approval Voting on the dichotomous preference domain, (b) the Borda Count is the only strategy-proof scoring rule on the dichotomous preference domain, and (c) if at least three individuals participate in the election, then the dichotomous preference domain is the unique maximal rich domain under which the Borda Count is strategy-proof.

Paths to stability for matching markets with couples

We study two-sided matching markets with couples and show that for a natural preference domain for couples, the domain of weakly responsive preferences, stable outcomes can always be reached by means of decentralized decision making. Starting from an arbitrary matching, we construct a path of matchings obtained from `satisfying' blocking coalitions that yields a stable matching. Hence, we establish a generalization of Roth and Vande Vate's (1990) result on path convergence to stability for decentralized singles markets. Furthermore, we show that when stable matchings exist, but preferences are not weakly responsive, for some initial matchings there may not exist any path obtained from `satisfying' blocking coalitions that yields a stable matching.

Bribe-proof rules in the division problem

The division problem consists of allocating an amount of a perfectly divisible good among a group of n agents with single-peaked preferences. A rule maps preference profiles into n shares of the amount to be allocated. A rule is bribe-proof if no group of agents can compensate another agent to misrepresent his preference and, after an appropriate redistribution of their shares, each obtain a strictly preferred share. We characterize all bribe-proof rules as the class of efficient, strategy-proof, and weak replacement monotonic rules. In addition, we identify the functional form of all bribe-proof and tops-only rules.

Some things couples always wanted to know about stable matchings (but were afraid to ask)

It is well-known that couples that look jointly for jobs in the same centralized labor market may cause instabilities. We demonstrate that for a natural preference domain for couples, namely the domain of responsive preferences, the existence of stable matchings can easily be established. However, a small deviation from responsiveness in one couple's preference relation that models the wish of a couple to be closer together may already cause instability. This demonstrates that the nonexistence of stable matchings in couples markets is not a singular theoretical irregularity. Our nonexistence result persists even when a weaker stability notion is used that excludes myopic blocking. Moreover, we show that even if preferences are responsive there are problems that do not arise for singles markets. Even though for couples markets with responsive preferences the set of stable matchings is nonempty, the lattice structure that this set has for singles markets does not carry over. Furthermore we demonstrate that the new algorithm adopted by the National Resident Matching Program to fill positions for physicians in the United States may cycle, while in fact a stable matchings does exist, and be prone to strategic manipulation if the members of a couple pretend to be single.

Stable condorcet rules

We consider the following allocation problem: A fixed number of public facilities must be located on a line. Society is composed of $N$ agents, who must be allocated to one and only one of these facilities. Agents have single peaked preferences over the possible location of the facilities they are assigned to, and do not care about the location of the rest of facilities. There is no congestion. In this context, we observe that if a public decision is a Condorcet winner, then it satisfies nice properties of internal and external stability. Though in many contexts and for some preference profiles there may be no Condorcet winners, we study the extent to which stability can be made compatible with the requirement of choosing Condorcet winners whenever they exist.

Stochastic dominance and absolute risk aversion

In this paper we propose the infimum of the Arrow-Pratt index of absolute risk aversion as a measure of global risk aversion of a utility function. We then show that, for any given arbitrary pair of distributions, there exists a threshold level of global risk aversion such that all increasing concave utility functions with at least as much global risk aversion would rank the two distributions in the same way. Furthermore, this threshold level is sharp in the sense that, for any lower level of global risk aversion, we can find two utility functions in this class yielding opposite preference relations for the two distributions.

Constrained school choice

Recently, several school districts in the US have adopted or consider adopting the Student-Optimal Stable Mechanism or the Top Trading Cycles Mechanism to assign children to public schools. There is clear evidence that for school districts that employ (variants of) the so-called Boston Mechanism the transition would lead to efficiency gains. The first two mechanisms are strategy-proof, but in practice student assignment procedures impede students to submit a preference list that contains all their acceptable schools. Therefore, any desirable property of the mechanisms is likely toget distorted. We study the non trivial preference revelation game where students can only declare up to a fixed number (quota) of schools to be acceptable. We focus on the stability of the Nash equilibrium outcomes. Our main results identify rather stringent necessary and sufficient conditions on the priorities to guaranteestability. This stands in sharp contrast with the Boston Mechanism which yields stable Nash equilibrium outcomes, independently of the quota. Hence, the transition to any of the two mechanisms is likely to come with a higher risk that students seek legal actionas lower priority students may occupy more preferred schools.

Use and users of electronic journals at Catalan universities: the results of a survey

Es presenten els resultats d’una enquesta sobre l’ús de revistes electròniques realitzada al professorat de les universitats que formen el Consorci de Biblioteques Universitàries de Catalunya (CBUC). Els resultats mostren un elevat grau de coneixement de la col·lecció de revistes electròniques entre el personal docent i investigador i una creixent preferència pel format electrònic en detriment de l’imprès. L’alt grau de coneixement i d’ús dels títols electrònics, i la preferència per aquest suport, comporten una elevada valoració de la col·lecció de revistes electròniques. Al mateix temps, la major part dels usuaris preveu un increment de l’ús dels títols electrònics durant els propers anys. Els resultats també confirmen la importància de la disciplina i de l’edat com a factors explicatius de l’ús de les revistes electròniques.

Uso y usuarios de revistas electrónicas en las universidades catalanas: resultados de una encuesta

Se presentan los resultados de una encuesta sobre el uso de revistas electrónicas realizada al profesorado de las universidades que forman el Consorci de Biblioteques Universitàries de Catalunya (CBUC). Los resultados muestran un elevado grado de conocimiento de la colección de revistas electrónicas entre el personal docente e investigador y una creciente preferencia por el formato electrónico en detrimento del impreso. El alto grado de conocimiento y uso de los títulos electrónicos, y la preferencia por este soporte, comportan una elevada valoración de la colección de revistas electrónicas. Al mismo tiempo, la mayor parte de los usuarios prevén un incremento en el uso de los títulos electrónicos durante los próximos años. Los resultados también confirman la importancia de la disciplina y de la edad como factores explicativos del uso de las revistas electrónicas.

Ús i usuaris de revistes electròniques a les universitats catalanes: resultats d’una enquesta

Es presenten els resultats d’una enquesta sobre l’ús de revistes electròniques realitzada al professorat de les universitats que formen el Consorci de Biblioteques Universitàries de Catalunya (CBUC). Els resultats mostren un elevat grau de coneixement de la col·lecció de revistes electròniques entre el personal docent i investigador i una creixent preferència pel format electrònic en detriment de l’imprès. L’alt grau de coneixement i d’ús dels títols electrònics, i la preferència per aquest suport, comporten una elevada valoració de la col·lecció de revistes electròniques. Al mateix temps, la major part dels usuaris preveu un increment de l’ús dels títols electrònics durant els propers anys. Els resultats també confirmen la importància de la disciplina i de l’edat com a factors explicatius de l’ús de les revistes electròniques.

Commuters' valuation of travel time variability in Barcelona

The value given by commuters to the variability of travel times is empirically analysed using stated preference data from Barcelona (Spain). Respondents are asked to choose between alternatives that differ in terms of cost, average travel time, variability of travel times and departure time. Different specifications of a scheduling choice model are used to measure the influence of various socioeconomic characteristics. Our results show that travel time variability.

Une approche psychanalytique de la notion de dangerosité. Violence et subjectivation : le risque de la rencontre

Après avoir situé la question de la dangerosité dans les perspectives psychiatriques actuelles, l'auteur propose de penser cette notion complexe dans un renversement du paradigme couramment admis : ainsi la référence à la dangerosité témoignerait-elle, au premier plan, de la part non symbolisée de la rencontre de la violence. Cette proposition prend appui dans un premier temps sur les propositions esquissées par M. Foucault dans sa compréhension du rapport à la violence et à la dangerosité. Puis, le recours au concept psychanalytique d'identification projective permet de proposer une modélisation clinique de la dangerosité, qui sera discutée à partir de deux observatoires dans le champ des violences sexuelles : celui d'une recherche menée auprès d'adolescents engagés dans des agirs sexuels violents et celui d'une pratique d'expertise judiciaire. First the author proposes to situate dangerousness's question in actual psychiatric field. Then, he proposes to think this complex notion into a reversal of dangerousness's paradigm: the reference to dangerousness will be thought as the expression of non-symbolized part through violence's meeting. This proposition relies in a first time on M. Foucault's propositions about a comprehension of the relation with violence and dangerousness. In a second time, the psychoanalytic concept of projective identification allows to propose clinical comprehension of dangerousness's notion. Two clinical situations about sexual violences will be asked in this plan: a research with Young sexual offenders and practice of judiciary evaluation.

Sympatric speciation in palms on an oceanic island.

The origin of species diversity has challenged biologists for over two centuries. Allopatric speciation, the divergence of species resulting from geographical isolation, is well documented. However, sympatric speciation, divergence without geographical isolation, is highly controversial. Claims of sympatric speciation must demonstrate species sympatry, sister relationships, reproductive isolation, and that an earlier allopatric phase is highly unlikely. Here we provide clear support for sympatric speciation in a case study of two species of palm (Arecaceae) on an oceanic island. A large dated phylogenetic tree shows that the two species of Howea, endemic to the remote Lord Howe Island, are sister taxa and diverged from each other well after the island was formed 6.9 million years ago. During fieldwork, we found a substantial disjunction in flowering time that is correlated with soil preference. In addition, a genome scan indicates that few genetic loci are more divergent between the two species than expected under neutrality, a finding consistent with models of sympatric speciation involving disruptive/divergent selection. This case study of sympatric speciation in plants provides an opportunity for refining theoretical models on the origin of species, and new impetus for exploring putative plant and animal examples on oceanic islands.

A Multicenter Randomized Clinical Trial of Primary Anastomosis or Hartmann's Procedure for Perforated Left Colonic Diverticulitis With Purulent or Fecal Peritonitis.

OBJECTIVES: : To evaluate the outcome after Hartmann's procedure (HP) versus primary anastomosis (PA) with diverting ileostomy for perforated left-sided diverticulitis. BACKGROUND: : The surgical management of left-sided colonic perforation with purulent or fecal peritonitis remains controversial. PA with ileostomy seems to be superior to HP; however, results in the literature are affected by a significant selection bias. No randomized clinical trial has yet compared the 2 procedures. METHODS: : Sixty-two patients with acute left-sided colonic perforation (Hinchey III and IV) from 4 centers were randomized to HP (n = 30) and to PA (with diverting ileostomy, n = 32), with a planned stoma reversal operation after 3 months in both groups. Data were analyzed on an intention-to-treat basis. The primary end point was the overall complication rate. The study was discontinued following an interim analysis that found significant differences of relevant secondary end points as well as a decreasing accrual rate (NCT01233713). RESULTS: : Patient demographics were equally distributed in both groups (Hinchey III: 76% vs 75% and Hinchey IV: 24% vs 25%, for HP vs PA, respectively). The overall complication rate for both resection and stoma reversal operations was comparable (80% vs 84%, P = 0.813). Although the outcome after the initial colon resection did not show any significant differences (mortality 13% vs 9% and morbidity 67% vs 75% in HP vs PA), the stoma reversal rate after PA with diverting ileostomy was higher (90% vs 57%, P = 0.005) and serious complications (Grades IIIb-IV: 0% vs 20%, P = 0.046), operating time (73 minutes vs 183 minutes, P < 0.001), hospital stay (6 days vs 9 days, P = 0.016), and lower in-hospital costs (US $16,717 vs US $24,014) were significantly reduced in the PA group. CONCLUSIONS: : This is the first randomized clinical trial favoring PA with diverting ileostomy over HP in patients with perforated diverticulitis.