The differential impact of friendship on cooperative and competitive coordination

Theory and Decision - Friendship is commonly assumed to reduce strategic uncertainty and enhance tacit coordination. However, this assumption has never been tested across two opposite poles of...     

Alpha as Ambiguity: Robust Mean‐Variance Portfolio Analysis

We derive the analogue of the classic Arrow–Pratt approximation of the certainty equivalent under model uncertainty as described by the smooth model of decision making under ambiguity of Klibanoff, Marinacci, and Mukerji (2005). We study its scope by deriving a tractable mean‐variance model adjusted for ambiguity and solving the corresponding portfolio allocation problem. In the problem with a risk‐free asset, a risky asset, and an ambiguous asset, we find that portfolio rebalancing in response to higher ambiguity aversion only depends on the ambiguous asset's alpha, setting the performance of the risky asset as benchmark. In particular, a positive alpha corresponds to a long position in the ambiguous asset, a negative alpha corresponds to a short position in the ambiguous asset, and greater ambiguity aversion reduces optimal exposure to ambiguity. The analytical tractability of the enhanced Arrow–Pratt approximation renders our model especially well suited for calibration exercises aimed at exploring the consequences of model uncertainty on equilibrium asset prices.     

Learning the two parameters of the Poisson–Dirichlet distribution with a forensic application

In forensic science, the rare type match problem arises when the matching characteristic from the suspect and the crime scene is not in the reference database; hence, it is difficult to evaluate the likelihood ratio that compares the defense and prosecution hypotheses. A recent solution consists of modeling the ordered population probabilities according to the two-parameter Poisson–Dirichlet distribution, which is a well-known Bayesian nonparametric prior, and plugging the maximum likelihood estimates of the parameters into the likelihood ratio. We demonstrate that this approximation produces a systematic bias that fully Bayesian inference avoids. Motivated by this forensic application, we consider the need to learn the posterior distribution of the parameters that governs the two-parameter Poisson–Dirichlet using two sampling methods: Markov Chain Monte Carlo and approximate Bayesian computation. These methods are evaluated in terms of accuracy and efficiency. Finally, we compare the likelihood ratio that is obtained by our proposal with the existing solution using a database of Y-chromosome haplotypes.     

Stereotypical Disease Inferences From Gay/Lesbian Versus Heterosexual Voices

Voice is a cue used to categorize speakers as members of social groups, including sexual orientation. We investigate the consequences of such voice-based categorization, showing that people infer stereotype-congruent disease likelihood on the basis of vocal information and without explicit information about the speaker’s sexual orientation. Study 1 and Study 2 reveal that participants attribute diseases to gay/lesbian and heterosexual men and women in line with stereotypes. Gay speakers were more likely to be associated with gay and female diseases, and lesbian speakers with male diseases. These findings demonstrate that likelihood to suffer from diseases is erroneously, but stereotypically, inferred from targets’ vocal information.     

Reflections on the application of the Delphi method: lessons from a case in public transport research

The paper outlines the author’s experience employing the Delphi method, using as an example a particular application of the Delphi in the field of public transport research. Attention is given to aspects such as the choice of method, selection of experts, design of questionnaires, interaction between survey coordinator and participants, and also the analysis of experts’ responses. Some of the challenges encountered during the survey, the way they were dealt with, and risk mitigation strategies used by the Delphi coordinator are highlighted too. The primary objective of this paper is to offer insights that can support other researchers or practitioners preparing to apply the Delphi methodology. Furthermore, the article contributes to the methodological debate by reflecting on the introduction of novel practices that can help overcome some typical pitfalls of the Delphi: a dedicated blog supporting the survey, safety-net questions, and a constant-sum type question.     

What happens if you single out? An experiment

We present an experiment investigating the effects of singling out an individual on trust and trustworthiness. We find that (a) trustworthiness falls if there is a singled out subject; (b) non-singled out subjects discriminate against the singled out subject when they are not responsible of the distinct status of this person; (c) under a negative frame, the singled out subject returns significantly less; (d) under a positive frame, the singled out subject behaves bimodally, either selecting very low or very high return rates. Overall, singling out induces a negligible effect on trust but is potentially disruptive for trustworthiness.     

Employment and unemployment patterns in the U.S. and Europe, 1973–1987

Employment trends in the United States and Europe are compared using Bureau of Labor Statistics data. These data set the stage for a discussion of the difference in employment growth between the U.S. and Europe. Also included are some elements that may partly explain the U.S. and European differences in job growth. In conclusion, labor market problems still remain even with the tremendous job growth in the U.S.     

Contextual Variation in Stereotype Content: An Investigation of Children's Central Tendency and Group Variability Judgements

Drawing upon self‐categorization theory, we predicted that the content of children's stereotypes concerning the gender ingroup would be contextually variable. Two studies are reported, each looking at five‐, seven‐, and 10‐year‐old children's stereotypes of the gender in‐group in two different contexts. Study 1 examined judgements of the perceived central tendency of the in‐group on specified dimensions. Study 2 addressed judgements of perceived variability within the gender in‐group on the same dimensions. Overall multivariate analysis of the data indicated that central tendency judgements were influenced by the context in which a group is considered, but that group variability judgements were not. Individual‐level analyses showed that the most typical pattern of response over the two conditions, in both Studies 1 and 2, was for children to provide consistent rather than varying judgements. However, in Study 1 (but not Study 2 ), among those children who changed their judgements, the nature of change was precisely as predicted by self‐categorization theory.