Homophily and Contagion Are Generically Confounded in Observational Social Network Studies

We consider processes on social networks that can potentially involve three factors: homophily, or the formation of social ties due to matching individual traits; social contagion, also known as social influence; and the causal effect of an individual's covariates on their behavior or other measurable responses. We show that, generically, all of these are confounded with each other. Distinguishing them from one another requires strong assumptions on the parametrization of the social process or on the adequacy of the covariates used (or both). In particular we demonstrate, with simple examples, that asymmetries in regression coefficients cannot identify causal effects, and that very simple models of imitation (a form of social contagion) can produce substantial correlations between an individual's enduring traits and their choices, even when there is no intrinsic affinity between them. We also suggest some possible constructive responses to these results.Comment: 27 pages, 9 figures. V2: Revised in response to referees. V3: Ditt

Combined Forward-Backward Asymmetry Measurements in Top-Antitop Quark Production at the Tevatron

The CDF and D0 experiments at the Fermilab Tevatron have measured the asymmetry between yields of forward- and backward-produced top and antitop quarks based on their rapidity difference and the asymmetry between their decay leptons. These measurements use the full data sets collected in proton-antiproton collisions at a center-of-mass energy of $\sqrt s =1.96$ TeV. We report the results of combinations of the inclusive asymmetries and their differential dependencies on relevant kinematic quantities. The combined inclusive asymmetry is $A_{\mathrm{FB}}^{t\bar{t}} = 0.128 \pm 0.025$. The combined inclusive and differential asymmetries are consistent with recent standard model predictions

Designing Documentary Informatics

In this paper, we describe a Research through Design inquiry about a speculative wedding documentation service, in the mode of the Quantified Self. We reflect on our design research, which included design ethnography, interviews, enactments of parts of the service, and the production of a concept brochure. In so doing, we explore the design of personal tracking as a documentary activity, one intended for longer-term self-expression and remembering – rather than simply to monitor, regulate and motivate a data-driven life. Developing the Lived Informatics discourse, we use our design-led inquiry to propose ‘Documentary Informatics’ as an alternative and longer-term design perspective on self-tracking tools

Problem solving in social interactions on the Internet: Rumor as social cognition

Rumor discourse has been conceptualized as an attempt to reduce anxiety and uncertainty via a process of social sensemaking. Fourteen rumors transmitted on various Internet discussion groups were observed and content analyzed over the life of each rumor With this (previously unavailable) more ecologically robust methodology, the intertwined threads of sensemaking and the gaining of interpretive control are clearly evident in the tapestry of rumor discourse. We propose a categorization of statements (the Rumor Interaction Analysis System) and find differences between dread rumors and wish rumors in anxiety-related content categories. Cluster analysis of these statements reveals a typology of voices (communicative postures) exhibiting sensemaking activities of the rumor discussion group, such as hypothesizing, skeptical critique, directing of activities to gain information, and presentation of evidence. These findings enrich our understanding of the long-implicated sensemaking function of rumor by clarifying the elements of communication that operate in rumor's social context