Group betweenness and co-betweenness: Inter-related notions of coalition centrality

Vertex betweenness centrality is a metric that seeks to quantify a sense of the importance of a vertex in a network in terms of its ‘control’ on the flow of information along geodesic paths throughout the network. Two natural ways to extend vertex betweenness centrality to sets of vertices are (i) in terms of geodesic paths that pass through at least one of the vertices in the set, and (ii) in terms of geodesic paths that pass through all vertices in the set. The former was introduced by Everett and Borgatti [Everett, M., Borgatti, S., 1999. The centrality of groups and classes. Journal of Mathematical Sociology 23 (3), 181–201], and called group betweenness centrality. The latter, which we call co-betweenness centrality here, has not been considered formally in the literature until now, to the best of our knowledge. In this paper, we show that these two notions of centrality are in fact intimately related and, furthermore, that this relationship may be exploited to obtain deeper insight into both. In particular, we provide an expansion for group betweenness in terms of increasingly higher orders of co-betweenness, in a manner analogous to the Taylor series expansion of a mathematical function in calculus. We then demonstrate the utility of this expansion by using it to construct analytic lower and upper bounds for group betweenness that involve only simple combinations of (i) the betweenness of individual vertices in the group, and (ii) the co-betweenness of pairs of these vertices. Accordingly, we argue that the latter quantity, i.e., pairwise co-betweenness, is itself a fundamental quantity of some independent interest, and we present a computationally efficient algorithm for its calculation, which extends the algorithm of Brandes [Brandes, U., 2001. A faster algorithm for betweenness centrality. Journal of Mathematical Sociology 25, 163] in a natural manner. Applications are provided throughout, using a handful of different communication networks, which serve to illustrate the way in which our mathematical contributions allow for insight to be gained into the interaction of network structure, coalitions, and information flow in social networks.     

The impact of migration on the well-being of transnational families: new data from sending communities in Mexico

We present results from a new study of the effects of migration to the USA on the well-being of transnational families in high emigration communities within Mexico. Our survey measured the well-being of family members in a variety of domains: economic, health, education, and child development for a representative sample drawn from high migration municipalities. Compared to those with no recent emigrants to the USA, Mexican households sending non-caregivers to the USA appear to gain economically without contributing to problems faced by children. However, when family caregivers migrate to the USA, the remaining members in Mexico struggle to meet the family's needs and children are more vulnerable to educational, emotional, and health problems. Children in households where a caregiver migrated were more likely to have frequent illnesses (10% vs. 3%, p<0.0001), chronic illness (7% vs. 3%, p=0.011), emotional problems (10% vs. 4%, p=0.006), and behavioral problems (17% vs. 10%, p=0.018) compared with children in households where the migrant was not a caregiver. Research, policy, and program implications of these findings are discussed.     

The paradox of multiple elections

Assume that voters must choose between voting yes (Y) and voting no (N) on three propositions on a referendum. If the winning combination is NYY on the first, second, and third propositions, respectively, the paradox of multiple elections is that NYY can receive the fewest votes of the 2³ = 8 combinations. Several variants of this paradox are illustrated, and necessary and sufficient conditions for its occurrence, related to the “incoherence” of support, are given. The paradox is shown, via an isomorphism, to be a generalization of the well-known paradox of voting. One real-life example of the paradox involving voting on propositions in California, in which not a single voter voted on the winning side of all the propositions, is given. Several empirical examples of variants of the paradox that manifested themselves in federal elections – one of which led to divided government – and legislative votes in the US House of Representatives, are also analyzed. Possible normative implications of the paradox, such as allowing voters to vote directly for combinations using approval voting or the Borda count, are discussed. Received: 31 July 1996 / Accepted: 1 October 1996     

Book Review: Strategic Management for Voluntary Nonprofit Organizations,by Roger Courtney. Routledge,New York, 2002

VOLUNTAS: International Journal of Voluntary and Nonprofit Organizations -     

Managing the deliberately mute

The contrast in communication styles and values between Gen-Xers, now mostly in their mid to late twenties, and forty- and fifty-somethings is obvious. Gen-Xers are focused on the assignment and the deadline; their goal is to do good work in a timely manner. But they are highly skeptical that enthusiasm has any influence on the outcome. When we question them about their taciturn manner, they all give us the same two reasons: They really don't care one way or the other and they're convinced that what they say doesn't matter anyhow. This may frustrate a manager charged with getting the buy-in or enthusiastic participation from the troops, but it's a fact. There are, however, ways to get Xers to talk--provided you really want their ideas and opinions and you acknowledge that you hear what they say. Here are the best techniques from those who successfully manage large numbers of the young, including young physicians: (1) Focus on what matters; (2) don't ask if you're not going to act on the feedback; (3) personalize your request for information; and (4) always do a worst case scenario when you need the buy-in.     

The importance of building alliances

This may come as a surprise to Gen-Xers, but on-the-job allies are a political necessity. Information and support from workplace alliances are vital to doing your job. Your peers, boss, subordinates, and even enemies, can and should be in your network of allies. How do you build alliances? It's accomplished by cultivating relationships based on mutual benefit and interest. Information and favors are traded on a quid pro quo basis. Your peers, subordinates, and boss have different needs but they share some goals with you. Goals are the common denominator. Consider the following ways to cultivate your network of allies: Be a reliable news source; offer feedback; be congenial; share expertise; consult; strive to be a role model; don't demand credit; don't wait for recognition; articulate your needs; share a hot idea; save face for someone; and connect people who can help each other.     

Do Irrelevant Commodities Matter?

We study how to evaluate allocations independently of individual preferences over unavailable commodities. We prove impossibility results that suggest that such evaluations encounter serious difficulties. This is related to the well known problem of performing international comparisons of standard of living across countries with different consumption goods. We show how possibility results can be retrieved with restrictions on the domain of preferences, on the application of the independence axiom, or on the set of allocations to be ranked. Such restrictions appear more plausible when the objects of evaluation are allocations of composite commodities, characteristics, or human functionings rather than ordinary commodities.     

Keeping Surveys Valid,Reliable, and Useful: A Tutorial

This tutorial focuses on how to produce reliable and generalizable data from random‐digit‐dialing (RDD) landline and cell phone surveys. The article notes that RDD response rates have declined and explores the impact of this pronounced decline. The tutorial addresses order, response mode, and many other biases, sample size, cooperation and response rates, weighting, and hybrid designs‐all using examples from risk analysis to illustrate the key points. The article ends with a brief review of the advantages and disadvantages of major Internet and paper surveys tools, and how these can be molded and sometimes combined in repeated, longitudinal, and other designs to answer questions about risk preferences and perceptions.