"Identifying causal effects attributable to network membership is a key challenge in empirical studies of social networks. In this article, we examine the consequences of endogeneity for inferences about the effects of networks on network members’ behavior. Using the House office lottery (in which newly elected members select their office spaces in a randomly chosen order) as an instrumental variable to estimate the causal impact of legislative networks on roll call behavior and cosponsorship decisions in the 105th–112th Houses, we find no evidence that office proximity affects patterns of legislative behavior. These results contrast with decades of congressional scholarship and recent empirical studies. Our analysis demonstrates the importance of accounting for selection processes and omitted variables in estimating the causal impact of networks."

"It's easy to imagine how we could make something worse than "Girls Around Me"—something much worse. Facebook encourages us to disclose a wide range of information about ourselves, including our religion and a photograph. Religion is obvious: "Yids Among Us" would obviously be one of the go-to tools of choice for Neo-Nazis. As for skin colour, ethnicity identification from face images is out there already. Want to go queer bashing? There's an algorithm out there for guessing sexual orientation based on the network graph of the target's facebook friends. It's probably possible to apply this sort of data mining exercise to determine whether a woman has had an abortion or is pro-choice.
"In the worst case, it's possible to envisage geolocation and data aggregation apps being designed to facilitate the identification and elimination of some ethnic or class enemy, not only by making it easy for users to track them down, but by making it easy for users to identify each other and form ad-hoc lynch mobs. (Hence my reference to the Rwandan Genocide earlier. Think it couldn't happen? Look at Iran and imagine an app written for the Basij to make it easy to identify dissidents and form ad-hoc goon squads to proactively hunt them down. Or any other organization in the post-networked world that has a social role corresponding to the Red Guards.)
"But as I said earlier, the app is not the problem. The problem is the deployment by profit-oriented corporations of behavioural psychology techniques to induce people to over-share information which can then be aggregated and disclosed to third parties for targeted marketing purposes."

Comment: Stross is not, sadly, exaggerating.

As Henry says, se non e vero, e bene trovato.

"How important are friendships in determining success by individuals and teams in complex competitive environments? By combining a novel data set on the dynamics of millions of ad hoc team-based competitions from the massively multiplayer online first person shooter (MMOFPS) Halo: Reach with ground-truth data on player demographics, play style, psychometrics and friendships derived from an anonymous online survey, we investigate the impact of friendship on performance in such competitive environments. We find that friendships play a fundamental role, leading to both improved individual and team performance---even after controlling for the overall expertise of the team---and increased pro-social behavior. Furthermore, because players structure their in-game activities around opportunities to play with friends, we show that friendships can largely be inferred directly from behavioral time series using common-sense heuristics. Algorithms that leverage the utility of friendships, without needing explicitly labeled (and thus private) data, are thus both possible and will likely improve many aspects of competition prediction and design."

"Why do some music styles gain mass popularity while others thrive in small niches? Banding Together explores this question and reveals the attributes that together explain the growth of twentieth-century American popular music. Drawing on a vast array of examples from sixty musical styles--ranging from rap and bluegrass to death metal and South Texas polka, and including several created outside the United States--Jennifer Lena uncovers the shared grammar that allows us to understand the cultural language and evolution of popular music.
"What are the common economic, organizational, ideological, and aesthetic traits among contemporary genres? Do genres follow patterns in their development? Lena discovers four dominant forms--Avant-garde, Scene-based, Industry-based, and Traditionalist--and two dominant trajectories that describe how American pop music genres develop. Outside the United States there exists a fifth form: the Government-purposed genre, which she examines in the music of China, Serbia, Nigeria, and Chile. Offering a rare analysis of how music communities operate, she looks at the shared obstacles and opportunities creative people face and reveals the ways in which people collaborate around ideas, artworks, individuals, and organizations that support their work."

"distrust of traditional lending institutions such as commercial banks led some borrowers to seek out brokers from their own communities whom they felt they could trust. But these brokers were operating under high-powered incentives to inflate rates and fees and guide borrowers towards subprime products even when they were eligible for cheaper alternatives. The trust that was placed in the brokers allowed them greater flexibility to respond to these incentives and left borrowers worse off than the would have been if they had been more suspicious or better aware of the incentive structures in place.
"Viewed in this manner, the subprime saga has some broader implications. From the point of view of a company operating in multiple local markets with a diverse customer base, the strategy of giving local employees or contractors the discretion to adjust prices can be very profitable. This is especially so if these employees appear trustworthy to their customers, but are not in fact deserving of such trust. As Groucho Marx is reputed to have said: 'The secret of life is honesty and fair-dealing. If you can fake that you've got it made.' For products involving frequent repeat purchases by the same customer, reputation effects and competition can limit the degree of price discrimination. But the purchase of a home is an infrequent transaction for most people, and the complexity of the loan product precludes easy comparison with alternatives on offer. Trust then becomes a key determinant of pricing and transaction volume, especially when strong and hidden incentives for the betrayal of trust are in place.
"Betrayal also leads to the erosion of trust over time. It could be argued that trust is one of our most valuable public goods, substantially lowering the costs of transacting. In the complete absence of trust, the resources that would need to be devoted to monitoring would be prohibitive and many organizations and markets would simply not exist. Trust also comes naturally to most of us, based on simple cues such as those revealed in Reid's interviews. High-powered incentives to secure and then betray such trust are therefore costly not just to the immediate victim, but also to the community at large. This may be one of the less visible consequences of the subprime crisis."

Why isn't the appropriate regulatory model that of phone companies, which also have network externalities (rather than production economies of scale), but are required to act as common (and mere) carriers?

"Complex problems in science, business, and engineering typically require some tradeoff between exploitation of known solutions and exploration for novel ones, where, in many cases, information about known solutions can also disseminate among individual problem solvers through formal or informal networks. Prior research on complex problem solving by collectives has found the counterintuitive result that inefficient networks, meaning networks that disseminate information relatively slowly, can perform better than efficient networks for problems that require extended exploration. In this paper, we report on a series of 256 Web-based experiments in which groups of 16 individuals collectively solved a complex problem and shared information through different communication networks. As expected, we found that collective exploration improved average success over independent exploration because good solutions could diffuse through the network. In contrast to prior work, however, we found that efficient networks outperformed inefficient networks, even in a problem space with qualitative properties thought to favor inefficient networks. We explain this result in terms of individual-level explore-exploit decisions, which we find were influenced by the network structure as well as by strategic considerations and the relative payoff between maxima. We conclude by discussing implications for real-world problem solving and possible extensions."

"Disentangling the effects of selection and influence is one of social science's greatest unsolved puzzles: Do people befriend others who are similar to them, or do they become more similar to their friends over time? Recent advances in stochastic actor-based modeling, combined with self-reported data on a popular online social network site, allow us to address this question with a greater degree of precision than has heretofore been possible. Using data on the Facebook activity of a cohort of college students over 4 years, we find that students who share certain tastes in music and in movies, but not in books, are significantly likely to befriend one another. Meanwhile, we find little evidence for the diffusion of tastes among Facebook friends—except for tastes in classical/jazz music. These findings shed light on the mechanisms responsible for observed network homogeneity; provide a statistically rigorous assessment of the coevolution of cultural tastes and social relationships; and suggest important qualifications to our understanding of both homophily and contagion as generic social processes."

It will be interested to see how they argue this isn't confounded six ways from Sunday.

"How does the composition of a population affect the adoption of health behaviors and innovations? Homophily—similarity of social contacts—can increase dyadic-level influence, but it can also force less healthy individuals to interact primarily with one another, thereby excluding them from interactions with healthier, more influential, early adopters. As a result, an important network-level effect of homophily is that the people who are most in need of a health innovation may be among the least likely to adopt it. Despite the importance of this thesis, confounding factors in observational data have made it difficult to test empirically. We report results from a controlled experimental study on the spread of a health innovation through fixed social networks in which the level of homophily was independently varied. We found that homophily significantly increased overall adoption of a new health behavior, especially among those most in need of it."

"The financial crisis of 2008 laid bare the hidden network of relationships in corporate governance: who owes what to whom, who will stand by whom in times of crisis, what governs the provision of credit when no one seems to have credit. This book maps the influence of these types of economic and social networks--communities of agents (people or firms) and the ties among them--on corporate behavior and governance. The empirically rich studies in the book are largely concerned with mechanisms for the emergence of governance networks rather than with what determines the best outcomes. The chapters identify “structural breaks”--privatization, for example, or globalization--and assess why powerful actors across countries behaved similarly or differently in terms of network properties and corporate governance.

The chapters examine, among other topics, the surprisingly heterogeneous network structures that contradict the common belief in a single Anglo-Saxon model; the variation in network trajectories among the formerly communist countries including China; signs of convergence in response to the common structural breaks in Europe; the growing structural power of women due to gains in gender diversity on corporate governance in Scandinavia; the “small world” of merger and acquisition activity in Germany and the United States; the properties of a global and transnational governance network; and application of agent-based models to understanding the emergence of governance."

"Disease awareness in infection dynamics can be modeled with adaptive contact networks whose rewiring rules reflect the attempt by susceptibles to avoid infectious contacts. Simulations of this type of models show an active phase with constant infected node density in which the interplay of disease dynamics and link rewiring prompts the convergence towards a well defined degree distribution, irrespective of the initial network topology. We develop a method to study this dynamic equilibrium and give an analytic description of the structure of the characteristic degree distributions and other network measures. The method applies to a broad class of systems and can be used to determine the steady-state topology of many other adaptive networks."

"Human populations are both highly cooperative and highly organized. Human interactions are not random but rather are structured in social networks. Importantly, ties in these networks often are dynamic, changing in response to the behavior of one's social partners. This dynamic structure permits an important form of conditional action that has been explored theoretically but has received little empirical attention: People can respond to the cooperation and defection of those around them by making or breaking network links. Here, we present experimental evidence of the power of using strategic link formation and dissolution, and the network modification it entails, to stabilize cooperation in sizable groups. Our experiments explore large-scale cooperation, where subjects’ cooperative actions are equally beneficial to all those with whom they interact. Consistent with previous research, we find that cooperation decays over time when social networks are shuffled randomly every round or are fixed across all rounds. We also find that, when networks are dynamic but are updated only infrequently, cooperation again fails. However, when subjects can update their network connections frequently, we see a qualitatively different outcome: Cooperation is maintained at a high level through network rewiring. Subjects preferentially break links with defectors and form new links with cooperators, creating an incentive to cooperate and leading to substantial changes in network structure. Our experiments confirm the predictions of a set of evolutionary game theoretic models and demonstrate the important role that dynamic social networks can play in supporting large-scale human cooperation."

"We study the structure of the social graph of active Facebook users, the largest social network ever analyzed. We compute numerous features of the graph including the number of users and friendships, the degree distribution, path lengths, clustering, and mixing patterns. Our results center around three main observations. First, we characterize the global structure of the graph, determining that the social network is nearly fully connected, with 99.91% of individuals belonging to a single large connected component, and we confirm the "six degrees of separation" phenomenon on a global scale. Second, by studying the average local clustering coefficient and degeneracy of graph neighborhoods, we show that while the Facebook graph as a whole is clearly sparse, the graph neighborhoods of users contain surprisingly dense structure. Third, we characterize the assortativity patterns present in the graph by studying the basic demographic and network properties of users. We observe clear degree assortativity and characterize the extent to which "your friends have more friends than you". Furthermore, we observe a strong effect of age on friendship preferences as well as a globally modular community structure driven by nationality, but we do not find any strong gender homophily. We compare our results with those from smaller social networks and find mostly, but not entirely, agreement on common structural network characteristics."

"The authors propose that a trade-off between network diversity and communications bandwidth regulates access to novel information because a more diverse network structure increases novelty at a cost of reducing information flow. Received novelty then depends on whether (a) the information overlap is small enough, (b) alters’ topical knowledge is shallow enough, and (c) alters’ knowledge stocks refresh slowly enough to justify bridging structural holes. Social network and e-mail content from an executive recruiting firm show that bridging ties can actually offer less novelty for these reasons, suggesting that the strength of weak ties and structural holes depend on brokers’ information environments."

"This paper inquires into structural explanations for triadic closure in networks of confidants with whom one discusses important personal matters. Building upon the assumption that meeting opportunities affect network characteristics, we primarily argue that the social contexts in which network members meet, substantially affect triadic closure. The main empirical findings are (a) that about sixty percent of the triads in core discussion networks are closed triads, which also means that a substantial part of one's strong relations is unconnected, and (b) that meeting network members in the same social contexts is an important condition for, but certainly does not guarantee triadic closure. Importantly, the specific characteristics of social contexts explain why sharing certain contexts positively affects triadic closure, while sharing other contexts does not."

I have no reason, to believe that this apparent peer-reviewed paper is actually a paid bit of PR for some undisclosed company, other than the fact that it was published by Elsevier.

"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." --- Not surprising, but I guess good to have confirmed.

Disappointing.  The content variables are all completely ad hoc (the structure variables are also ad hoc, but traditional), so we really have no idea of what is being found here.  And there is no assessment of uncertainty at all.  And, for the love of Gauss, stop using R^2 like that!

Did I really use "probably" twice in one sentence that way?  Sigh.

"...Twitter's distinction between different types o interactions allows us to establish a parallelism between online and offline social networks: personal interactions are more likely to occur on internal links of groups (the weakness of strong ties), events transmitting information pass preferentially through links connecting different groups or even more through users acting as bridges between groups (the strength of weak ties)."

"As a consequence of the rising interest in longitudinal social networks and their analysis, there is also an increasing demand for tools to visualize them. We argue that similar adaptations of state-of-the-art graph-drawing methods can be used to visualize both, longitudinal networks and predictions of stochastic actor-oriented models (SAOMs), the most prominent approach for analyzing such networks. The proposed methods are illustrated on a longitudinal network of acquaintanceship among university freshmen."

At last!

Some interesting observations.  (But repeat after me: the link distribution of weblogs is not a power law.)

" These findings underscore the fundamental difference between information spread and other contagion processes: despite multiple opportunities for infection within a social group, people are less likely to become spreaders of information with repeated exposure."

"Just as neurons interconnect in networks that create structured thoughts beyond the ken of any individual neuron, so people spontaneously organize themselves into groups to create emergent organizations that no individual may intend, comprehend, or even perceive. ... two experimental paradigms in which we attempt to build predictive bridges between the beliefs, goals, and cognitive capacities of individuals and patterns of behavior at the group level, showing how the members of a group dynamically allocate themselves to resources and how innovations diffuse through a social network. Agent-based computational models have provided useful explanatory and predictive accounts. Together, the models and experiments point to tradeoffs between exploration and exploitation—that is, compromises between individuals using their own innovations and using innovations obtained from their peers—and the emergence of group-level organizations..."

"This article engages with problems that are usually opaque: What trajectories do scientific debates assume, when does a scientific community consider a proposition to be a fact, and how can we know that? We develop a strategy for evaluating the state of scientific contestation on issues. The analysis builds from Latour’s black box imagery, which we observe in scientific citation networks. We show that as consensus forms, the importance of internal divisions to the overall network structure declines. We consider substantive cases that are now considered facts, such as the carcinogenicity of smoking and the non-carcinogenicity of coffee. We then employ the same analysis to currently contested cases: the suspected carcinogenicity of cellular phones, and the relationship between vaccines and autism. Extracting meaning from the internal structure of scientific knowledge carves a niche for renewed sociological commentary on science..."

"a simple model of the evolution of online communities. This model describes (a) the time evolution of users’ activity in a web service, e.g., the time evolution of the number of online friends or written posts, (b) the time evolution of the degree distribution of a social network, and (c) the time evolution of the number of active users of a web service. In the second part of the paper we investigate the influence of the users’ lifespan (i.e., the total time in which they are active in an online community) on the process of rumor propagation in evolving social networks. Viral marketing is an important application of such method of information propagation."

"A novel paradigm was developed to study the behavior of groups of networked people searching a problem space. The authors examined how different network structures affect the propagation of information in laboratory-created groups. Participants made numerical guesses and received scores that were also made available to their neighbors in the network. The networks were compared on speed of discovery and convergence on the optimal solution. One experiment showed that individuals within a group tend to converge on similar solutions even when there is an equally valid alternative solution. Two additional studies demonstrated that the optimal network structure depends on the problem space being explored, with networks that incorporate spatially based cliques having an advantage for problems that benefit from broad exploration, and networks with greater long-range connectivity having an advantage for problems requiring less exploration."

"An increasing number of scholars are using longitudinal social network data to try to obtain estimates of peer or social influence effects. These data may provide additional statistical leverage, but they can introduce new inferential problems. In particular, while the confounding effects of homophily in friendship formation are widely appreciated, homophily in friendship retention may also confound causal estimates of social influence in longitudinal network data. We provide evidence for this claim in a Monte Carlo analysis of the statistical model used by Christakis, Fowler, and their colleagues in numerous articles estimating "contagion" effects in social networks. Our results indicate that homophily in friendship retention induces significant upward bias and decreased coverage levels in the Christakis and Fowler model if there is non-negligible friendship attrition over time."

Shorter AT: nothing good can come of throwing away part of your interaction structure.

"A model for network panel data is discussed, based on the assumption that the observed data are discrete observations of a continuous-time Markov process on the space of all directed graphs on a given node set, in which changes in tie variables are independent conditional on the current graph. The model for tie changes is parametric and designed for applications to social network analysis, where the network dynamics can be interpreted as being generated by choices made by the social actors represented by the nodes of the graph. An algorithm for calculating the Maximum Likelihood estimator is presented, based on data augmentation and stochastic approximation. An application to an evolving friendship network is given and a small simulation study is presented which suggests that for small data sets the Maximum Likelihood estimator is more efficient than the earlier proposed Method of Moments estimator."

Of course, saying "we assume that correlated effects are absent" is, in this context at least, very much a "we assume we have a can opener" move.

Exit, voice, loyalty, and social-network lock-in: "Facebook is like a beloved national homeland poisoned by a corrupt and unyielding government. As in real life, a few people like Dan will respond to such a situation by ritual suicide. Others will choose to exercise voice and or soldier on with resigned loyalty to life under the boot. But in real life, a significant number of people choose to defect, to flee. That’s different from just “deleting” yourself. And to do that, you have to have somewhere to go. Plenty of us would choose such an exile from the dictatorship of Facebook were there a welcoming neighbor nearby to which we could escape with our friends and families..."

"An introduction to a vast but uncompleted survey of world history, this article argues that the study of the changing relationships among cities, states and trust networks can help us understand key elements of the emergence of our modern world. Beginning in ancient Uruk in modern-day Iraq, roughly five thousand years ago, the essay defines each of its central categories: city, state and trust network. It poses four questions to be pursued throughout the rest of the study. What determines the degree of segregation or integration of cities and states? What determines the relative dominance of cities and states? What determines the extent of separation or integration between cities or states, on one side, and trust networks on the other? What difference do these variable configurations make to the quality of ordinary people’s lives?"

On the National Review holding a symposium on black unemployment with all white symposiasts, none of them an expert on the subject: "That's fine, it's just amusing to see a magazine opposed to affirmative action exemplifying why such a policy might be needed. Rather than pick for the most qualified minds on the subject, it seems like they went with people to whom the magazine has social and ideological ties, and those people happened to all be white. It's certainly good that NRO is treating an issue like black unemployment seriously, but the symposium itself is a pretty good example of something that affects black unemployment in the real world: how black people, even those with impeccable qualifications, get overlooked based on formal and informal social networks rather than simply not being right for the job."

" focus on Flickr and Last.fm, two social media systems in which we can relate the tagging activity of the users with an explicit representation of their social network. We show that a substantial level of local lexical and topical alignment is observable among users who lie close to each other in the social network. We introduce a null model that preserves user activity while removing local correlations, allowing us to disentangle the actual local alignment between users from statistical effects due to the assortative mixing of user activity and centrality in the social network. ... suggests that users with similar topical interests are more likely to be friends, and therefore semantic similarity measures among users based solely on their annotation metadata should be predictive of social links. We test this ... on the Last.fm data set ... social network constructed from semantic similarity captures actual friendship [better] than Last.fm's suggestions based on listening patterns"

Why had I not heard of this book?!?

You could hardly ask for a better set of instructors, and Whistler is beautiful. The only way to improve this would be to drop the "Bayesian" bit.

"draws on several centuries of political and social thought to show how globalization is best understood in terms of a power inherent in social relations, which he calls network power. Using this framework, he demonstrates how our standards of social coordination both gain in value the more they are used and undermine the viability of alternative forms of cooperation. A wide range of examples are discussed, from the spread of English and the gold standard to the success of Microsoft and the operation of the World Trade Organization, to illustrate how global standards arise and falter. The idea of network power supplies a coherent set of terms and conceptsapplicable to individuals, businesses, and countries alikethrough which we can describe the processes of globalization as both free and forced. The result is a sophisticated and novel account of how globalization, and politics, work." - Initial impression: Tom Slee did this better.

I especially look forward to reading the bits about Larry Summers.

Ahhh, the review paper everyone's been so busy with.

This point came up at the NIPS networks workshop ("why don't we just engineer better political movements from our online social networks?"), and I wish I'd had the wit to respond like this.

"sociological theories consider murder an outcome of the differential distribution of individual, neighborhood, or social characteristics ... explain variation in aggregate homicide rates [but not] the social order of murder [:] who kills whom, when, where, and for what reason. ... gang murder is best understood not by ... its individual determinants but by ... the social networks of action and reaction that create it. ... the social structure of gang murder is defined by the manner in which social networks are constructed and by people's placement in them. ... uses a network approach and incident‐level homicide records to recreate and analyze the structure of gang murders in Chicago. ... individual murders between gangs create an institutionalized network of group conflict, net of any individual's participation or motive. Within this network, murders spread through an epidemic‐like process of social contagion ...."

I'm there.

CMU, October 19. Free but registration req'd.

"The aim of this paper is to study whether a child's schooling choices are affected by the schooling choices of other children. Identification is based on a randomized targeted intervention that grants a cash subsidy conditional on school attendance to a subgroup of eligible children within small rural villages in Mexico (PROGRESA). This policy change spills over to ineligible children if social interactions are relevant. Results indicate that the eligible children tend to attend school more frequently, and the ineligible children acquire more schooling when the subsidy is introduced in their local village. Moreover, the overall effect of PROGRESA on eligible children is the sum of a direct effect due to cash transfers and an indirect effect due to changes in peer group schooling. Interestingly, the social interactions effect is almost as important as the direct effect."

Need to re-examine the polarization bit. I suspect it's not actually incompatible with a sensible story about how polarization has actually grown.

Well, their power law estimation is bad, of course, but more to the point I don't think they're really dealing with an interesting version of the thesis they set out to undermine. (At the very least: even if geography was irrelevant for Internet users, the latter are not uniformly distributed geographically.) The pictures of the diffusion of baby names are cool, though.