Attention on Weak Ties in Social and Communication Networks

Granovetter's weak tie theory of social networks is built around two central hypotheses. The first states that strong social ties carry the large majority of interaction events; the second maintains that weak social ties, although less active, are often relevant for the exchange of especially important information (e.g., about potential new jobs in Granovetter's work). While several empirical studies have provided support for the first hypothesis, the second has been the object of far less scrutiny. A possible reason is that it involves notions relative to the nature and importance of the information that are hard to quantify and measure, especially in large scale studies. Here, we search for empirical validation of both Granovetter's hypotheses. We find clear empirical support for the first. We also provide empirical evidence and a quantitative interpretation for the second. We show that attention, measured as the fraction of interactions devoted to a particular social connection, is high on weak ties --- possibly reflecting the postulated informational purposes of such ties --- but also on very strong ties. Data from online social media and mobile communication reveal network-dependent mixtures of these two effects on the basis of a platform's typical usage. Our results establish a clear relationships between attention, importance, and strength of social links, and could lead to improved algorithms to prioritize social media content

Excludability: A laboratory study on forced ranking in team production

Exclusion has long been employed as a common disciplinary measure against defectors, both at work and in social life. In this paper, we study the effect of excludability - exclusion of the lowest contributor - on contributions in three different team production settings. We demonstrate theoretically and experimentally that excludability increases contributions. Excludability is particularly effective in production settings where the average or maximum effort determines team production. In these settings, we observe almost immediate convergence to full contribution. In settings where the minimum effort determines team production, excludability leads to a large increase in contributions only if the value of the excluded individual's contribution to the public good is redistributed among the included individuals

Conflicts with Multiple Battlefields

This paper examines conflicts in which performance is measured by the players' success or failure in multiple component conflicts, commonly termed “battlefields”. In multi-battlefield conflicts, behavioral linkages across battlefields depend both on the technologies of conflict within each battlefield and the nature of economies or diseconomies in how battlefield out-comes and costs aggregate in determining payoffs in the overall conflict.conflict, contest, battlefield, Colonel Blotto Game, auction, lottery

THE WEAKEST LINK HYPOTHESIS FOR ADAPTIVE CAPACITY: AN EMPIRICAL TEST

Yohe and Tol (2001) built an indexing method for vulnerability based on the hypothesis that the adaptive capacity for any system facing a vector of external stresses could be explained by the weakest of eight underlying determinants – the so-called “weakest link” hypothesis. Subsequent work supported the hypothesis by analogy from other contexts, but we now offer perhaps the first attempt to explore its validity through empirical means. We estimate a structural form designed to accommodate the full range of possible interactions across determinants. The perfect complement case of the pure “weakest-link” formulation lies on one extreme, and the perfect substitute case where each determinant can compensate for all others at constant rates is the other limiting case. For vulnerability to natural disasters, infant mortality and drinking water treatment, we find qualified support for a modified weakest link hypothesis: the weakest indicator plays an important role, but is not essential because other factors can compensate (with increasing difficulty). For life expectancy, sanitation and nutrition, we find a relationship that is close to linear – the perfect substitute case where the various determinants of adaptive capacity can compensate for each other. Moreover, we find another source of diversity in the assessment of vulnerability, since the factors from which systems draw to create adaptive capacity are different for different risks.Adaptive capacity, vulnerability, weakest-link hypothesis, substitution

WEAK LINKS, GOOD SHOTS AND OTHER PUBLIC GOOD GAMES: BUILDING ON BBV

We suggest an alternative way of analyzing the canonical Bergstrom-Blume-Varian model of non-cooperative voluntary contributions to a public good that avoids the proliferation of dimensions as the number of players is increased. We exploit this approach to analyze models in which the aggregate level of public good is determined as a more general social composition function of individual gifts – specifically, as a generalized CES form – rather than as an unweighted sum as well as the weakest-link and best-shot models suggested by Hirshleifer. In each case, we characterize the set of equilibria, in some cases establishing existence of a unique equilibrium as well as briefly pointing out some interesting comparative static properties. We also study the weakest-link and best-shot limits of the CES composition function and show how the former can be used for equilibrium selection and the latter to show that equilibria of some better-shot games are identical to those of the much simpler best-shot game.non cooperative games, public goods, weakest links, best shots

Characterizations of Super-regularity and its Variants

Convergence of projection-based methods for nonconvex set feasibility problems has been established for sets with ever weaker regularity assumptions. What has not kept pace with these developments is analogous results for convergence of optimization problems with correspondingly weak assumptions on the value functions. Indeed, one of the earliest classes of nonconvex sets for which convergence results were obtainable, the class of so-called super-regular sets introduced by Lewis, Luke and Malick (2009), has no functional counterpart. In this work, we amend this gap in the theory by establishing the equivalence between a property slightly stronger than super-regularity, which we call Clarke super-regularity, and subsmootheness of sets as introduced by Aussel, Daniilidis and Thibault (2004). The bridge to functions shows that approximately convex functions studied by Ngai, Luc and Th\'era (2000) are those which have Clarke super-regular epigraphs. Further classes of regularity of functions based on the corresponding regularity of their epigraph are also discussed.Comment: 15 pages, 2 figure

INFECTIOUS DISEASE, DEVELOPMENT, AND CLIMATE CHANGE: A SCENARIO ANALYSIS

We study the effects of development and climate change on infectious disease in Sub-Saharan Africa. Infant mortality and infectious disease are close related, but there are better data for the former. In an international cross-section, per capita income, literacy, and absolute poverty significantly affect infant mortality. We use scenarios of these three determinants, and of climate change to project the future incidence of malaria, assuming it to change proportionally to infant mortality. Malaria deaths will first increase, because of population growth and climate change, but then fall, because of development. This pattern is robust to the choice of scenario, parameters, and starting conditions; and it holds for diarrhoea, schistosomiasis, and dengue fever as well. However, the time and level of the mortality peak is very sensitive to assumptions. Climate change is important in the medium term, but dominated in the long term by development. As climate can only be changed with a substantial delay, development is the preferred strategy to reduced infectious diseases, even if that is exacerbated by climate change.Development, infectious disease, climate change, Sub-Saharan Africa, malaria

Towards Enhanced Usability of IT Security Mechanisms - How to Design Usable IT Security Mechanisms Using the Example of Email Encryption

Nowadays, advanced security mechanisms exist to protect data, systems, and networks. Most of these mechanisms are effective, and security experts can handle them to achieve a sufficient level of security for any given system. However, most of these systems have not been designed with focus on good usability for the average end user. Today, the average end user often struggles with understanding and using security mecha-nisms. Other security mechanisms are simply annoying for end users. As the overall security of any system is only as strong as the weakest link in this system, bad usability of IT security mechanisms may result in operating errors, resulting in inse-cure systems. Buying decisions of end users may be affected by the usability of security mechanisms. Hence, software provid-ers may decide to better have no security mechanism then one with a bad usability. Usability of IT security mechanisms is one of the most underestimated properties of applications and sys-tems. Even IT security itself is often only an afterthought. Hence, usability of security mechanisms is often the after-thought of an afterthought. This paper presents some guide-lines that should help software developers to improve end user usability of security-related mechanisms, and analyzes com-mon applications based on these guidelines. Based on these guidelines, the usability of email encryption is analyzed and an email encryption solution with increased usability is presented. The approach is based on an automated key and trust man-agement. The compliance of the proposed email encryption solution with the presented guidelines for usable security mechanisms is evaluated