Geography of Twitter networks

The paper examines the influence of geographic distance, national boundaries, language, and frequency of air travel on the formation of social ties on Twitter, a popular micro-blogging website. Based on a large sample of publicly available Twitter data, our study shows that a substantial share of ties lies within the same metropolitan region, and that between regional clusters, distance, national borders and language differences all predict Twitter ties. We find that the frequency of airline flights between the two parties is the best predictor of Twitter ties. This highlights the importance of looking at pre-existing ties between places and people.     

Drivers of Youth Labour Market Integration Across European Regions

Territorial disparities and youth labour markets have been often considered as separated themes, due to challenges in data availability. Comparative regional or sub-regional research on youth labour market integration (YLMI) have been therefore scarce. In this article, we address this gap by presenting a composite measure of YLMI that covers a wide range of indicators and sheds light on the EU territorial divide of young peoples’ opportunities at regional level. In order to build the YLMI index, we use benefit-of-the-doubt-weighting, a seminal methodology on composite indicators (CI) that combines sequence with conditional weights based on the range of each sub-indicator. To proof the usefulness of YLMI, we analyze the evolution of regional YLMI in the EU before and after the economic crisis; and the trends of homogenization or differentiation across EU territories. Furthermore, we investigate to what extent employment conditions, skills supply and technological resources explain cross-regional variations in YLMI.

     

Neural Correlates of Pathological Gamblers Preference for Immediate Rewards During the Iowa Gambling Task: An fMRI Study

The Iowa Gambling Task (IGT) involves exploratory learning via rewards and penalties, where most advantageous task performance requires subjects to forego potential large immediate rewards for small longer-term rewards to avoid larger punishments. Pathological gambling (PG) subjects perform worse on the IGT compared to controls, relating to their persistence at high risk decisions involving the continued choice of potential large immediate rewards despite experiencing larger punishments. We wished to determine if neural processing of risk and reward within striatal and frontal cortex is associated with this behaviour observed in PG. Functional magnetic resonance imaging (fMRI) was used to assess brain activity in response to a computerized version of the IGT. Thirteen male PG subjects with no active comorbidities were compared to 13 demographically matched control subjects. In agreement with previous behavioural studies, PG subjects performed worse on the IGT and made more high-risk choices compared to controls, particularly after experiencing wins and losses. During high-risk gambling decisions, fMRI demonstrated that PG subjects exhibited relatively increased frontal lobe and basal ganglia activation, particularly involving the orbitofrontal cortex (OFC), caudate and amygdala. Increased activation of regions encompassing the extended reward pathway in PG subjects during high risk choices suggests that the persistence of PG may be due to the increased salience of immediate and greater potential monetary rewards relative to lower monetary rewards or potential future losses. Whether this over activation of the reward pathway is associated with the development of PG warrants further investigation.     

Old and novel methods for estimating Feral Pigeons (Columba livia f. domestica) population size: a reply to Amoruso et al. (2013)

In a recent paper Amoruso et al. (2013) proposed a novel method for estimating population size of Feral Pigeons, the Superimposed Urban Strata (SUS) method. In our reply we firstly comment on the lack of a complete review of the available literature. Secondly we point out that the SUS method does not account for birds detection probability and thus it is just a simple index of abundance as many others proposed in recent years. Thirdly, we question the approach used by the authors to evaluate the reliability of their method. To conclude, we believe that the SUS method is not truly innovative and that further investigations are needed before considering it as a reliable way for estimating Feral Pigeons populations size.     

The Role of Internal Health Locus of Control in Relation to Self-Rated Health in Older Adults

ABSTRACT

The present study examined how internal health locus of control is associated with older adults’ self-rated health. Multivariate analyses with older participants (aged ≥ 60) in the MIDUS II (n = 1,533) showed that internal health locus of control was not only directly associated with positive ratings of health but also interacted with gender and race. The positive impact of internal health locus of control on self-rated health was particularly greater in females and Whites than their counterparts. Findings highlight the important role of internal health locus of control in the psychological mechanism of health and call attention to group-specific strategies for health promotion.     

Berry–Esseen type bounds for trimmed U-statistics

Trimmed U  -statistics can be constructed in two different ways: by basing the statistic on a trimmed sample or by averaging the trimmed set of kernel values. Mild conditions are given to ensure the rate of convergence to normality is O(n^-1/2)$\mathrm{O}(n^{-1/2})$ in both cases.     

Strategic Consumer Cooperation in a Name‐Your‐Own‐Price Channel

Supplier reluctance to openly advertise highly discounted products on the Internet has stimulated development of “opaque” name‐Your‐Own‐Price sales channels. Unfortunately (for suppliers), there is significant potential for online consumers to exploit these channels through collaboration in social networks. In this paper, we study three possible forms of consumer collaboration: exchange of bid result information, coordinated bidding, and coordinated bidding with risk pooling. We propose an egalitarian total utility maximizing mechanism for coordination and risk pooling in a bidding club and describe characteristics of consumers for whom participation in the club makes sense. We show that, in the absence of risk pooling, a plausible bidding club strategy using just information exchange gives almost the same benefits to consumers as coordinated bidding. In contrast, coordinated bidding with risk pooling can lead to significantly increased benefits for consumers. The benefits of risk pooling are highest for consumers with a low tolerance to risk. We also demonstrate that suppliers that actively adjust for such strategic consumer behavior can reduce the impact on their businesses and, under some circumstances, even increase revenues.     

Nonparametric regression estimation of conditional tails: the random covariate case

We present families of nonparametric estimators for the conditional tail index of a Pareto-type distribution in the presence of random covariates. These families are constructed from locally weighted sums of power transformations of excesses over a high threshold. The asymptotic properties of the proposed estimators are derived under some assumptions on the conditional response distribution, the weight function and the density function of the covariates. We also introduce bias-corrected versions of the estimators for the conditional tail index, and propose in this context a consistent estimator for the second-order tail parameter. The finite sample performance of some specific examples from our classes of estimators is illustrated with a small simulation experiment.