Doubly reweighted estimators for the parameters of the multivariate t-distribution

The t-distribution (univariate and multivariate) has many useful applications in robust statistical analysis. The parameter estimation of the t-distribution is carried out using maximum likelihood (ML) estimation method, and the ML estimates are obtained via the Expectation-Maximization (EM) algorithm. In this article, we will use the maximum Lq-likelihood (MLq) estimation method introduced by Ferrari and Yang (2010 Ferrari, D., and Y. Yang. 2010. Maximum lq-likelihood estimation. The Annals of Statistics 38 (2):753–83.[Crossref], [Web of Science ®] , [Google Scholar]) to estimate all the parameters of the multivariate t-distribution. We modify the EM algorithm to obtain the MLq estimates. We provide a simulation study and a real data example to illustrate the performance of the MLq estimators over the ML estimators.     

A meta-analytic examination of the effects of the agentic and affiliative aspects of extraversion on leadership outcomes

Building on previous research that has shown that extraversion is the strongest Big Five personality predictor of effective leadership, the present study employed meta-analytic procedures to examine the independent effects of the two main aspects of extraversion—agency and affiliation—on leadership outcomes (transformational leadership and leadership effectiveness). Results showed that it is specifically the agentic aspect of extraversion that has a positive impact on leadership, whereas the affiliative aspect is unrelated to transformational leadership and negatively related to leadership effectiveness. Additionally, we demonstrate that assessing extraversion in terms of these two aspects leads to substantial improvements in predictive validity relative to broad measures of extraversion. Limitations associated with common method bias and modest effect sizes notwithstanding, our findings inform theory on specifically why it is that extraverts are perceived as better leaders than introverts. We also discuss practical implications for how to select and develop leaders in organisational settings and outline the types of organisations in which agency measures are likely to be most useful for selection purposes.     

Static-dynamic uncertainty strategy for a single-item stochastic inventory control problem

We consider a single-stage inventory system facing non-stationary stochastic demand of the customers in a finite planning horizon. Motivated by the practice, the replenishment times need to be determined and frozen once and for all at the beginning of the horizon while decisions on the exact replenishment quantities can be deferred until the replenishment time. This operating scheme is refereed to as a “static-dynamic uncertainty” strategy in the literature [3]. We consider dynamic fixed-ordering and linear end-of-period holding costs, as well as dynamic penalty costs, or service levels. We prove that the optimal ordering policy is a base stock policy for both penalty cost and service level constrained models. Since an exponential exhaustive search based on dynamic programming yields the optimal ordering periods and the associated base stock levels, it is not possible to compute the optimal policy parameters for longer planning horizons. Thus, we develop two heuristics. Numerical experiments show that both heuristics perform well in terms of solution quality and scale-up efficiently; hence, any practically relevant large instance can be solved in reasonable time. Finally, we discuss how our results and heuristics can be extended to handle capacity limitations and minimum order quantity considerations.     

Arrovian impossibilities in aggregating preferences over non-resolute outcomes

Let A be a set of alternatives whose power set is . Elements of are interpreted as non-resolute outcomes. We consider the aggregation of preference profiles over into a (social) preference over . In case we allow individuals to have any complete and transitive preference over , Arrow’s impossibility theorem naturally applies. However, the Arrovian impossibility prevails, even when the set of admissible preferences over is severely restricted. In fact, we identify a mild “regularity” condition which ensures the dictatoriality of a domain. Regularity is compatible with almost all standard extension axioms of the literature. Thus, we interpret our results as the strong prevalence of Arrow’s impossibility theorem in aggregating preferences over non-resolute outcomes. This paper is part of a project entitled “Social Perception—A Social Choice Perspective”, supported by Istanbul Bilgi University Research Fund. It has been completed while Remzi Sanver was visiting Ecole Polytechnique, Paris. We are grateful to both institutions. We thank Nick Baigent, two anonymous referees and an anonymous associate editor for their valuable comments.     

Adolescents’ perceptions of social risk and prosocial tendencies: Developmental change and individual differences

Many prosocial behaviors involve social risks such as speaking out against a popular opinion, bias, group norm, or authority. However, little is known about whether adolescents’ prosocial tendencies develop over time with their perceptions of social risks. This accelerated longitudinal study used within-subject growth-curve analyses to test the link between adolescents' prosocial tendencies and social risk perceptions. Adolescents completed self-reports annually for 3 years (N = 893; M_age = 12.30 years, 10–14 years at Wave 1, and 10–17 years across the full study period; 50% girls, 33% White non-Latinx, 27% Latinx, 20% African American, 20% mixed/other race). The association between social risk tolerance and prosocial tendencies changed significantly across adolescence. Specifically, for younger adolescents, more prosocial tendencies were associated significantly with less social risk tolerance, whereas for relatively older adolescents, more prosocial tendencies were associated marginally with more social risk tolerance. Additional individual differences by empathy (but not sensation seeking) emerged. These findings suggest that prosocial tendencies across adolescence may be associated with an underlying ability to tolerate social risks.