Data sharing, research ethics, and incentives must improve

Homophily can put minority groups at a disadvantage by restricting their ability to establish links with a majority group or to access novel information. Here, we show how this phenomenon can influence the ranking of minorities in examples of real-world networks with various levels of heterophily and homophily ranging from sexual contacts, dating contacts, scientific collaborations, and scientific citations. We devise a social network model with tunable homophily and group sizes, and demonstrate how the degree ranking of nodes from the minority group in a network is a function of (i) relative group sizes and (ii) the presence or absence of homophilic behaviour. We provide analytical insights on how the ranking of the minority can be improved to ensure the representativeness of the group and correct for potential biases. Our work presents a foundation for assessing the impact of homophilic and heterophilic behaviour on minorities in social networks.

Although considerable research has concentrated on online campaigning, it is still unclear how politicians use different social media platforms in political communication. Focusing on the German federal election campaign 2013, this article investigates whether election candidates address the topics most important to the mass audience and to which extent their communication is shaped by the characteristics of Facebook and Twitter. Based on open-ended responses from a representative survey conducted during the election campaign, we train a human-interpretable Bayesian language model to identify political topics. Applying the model to social media messages of candidates and their direct audiences, we find that both prioritize different topics than the mass audience. The analysis also shows that politicians use Facebook and Twitter for different purposes. We relate the various findings to the mediation of political communication on social media induced by the particular characteristics of audiences and sociotechnical environments.Keywords cross-media analysis, language models, online campaigning, social media, text analysis Social media have become ubiquitous communication channels for candidates during election campaigns. Platforms like Facebook and Twitter enable candidates to directly reach out to voters, mobilize supporters, and influence the public agenda. These fundamental changes in political communication therefore present election candidates with a widened range of strategic choices. Should candidates address the topics most important to a mass audience? Should they tailor their messages to the specific habits and audiences on social media platforms? Although academic research on social media campaigning has flourished in the past several years (Boulianne, 2016;Jungherr, 2016b), it is still unclear which topics politicians address on these platforms, since previous research mostly concentrated on meta data generated by the use of communication conventions such as retweets, @-mentions, likes, or hashtags. Understanding the ways in which politicians Sebastian Stier, Arnim Bleier, and Haiko Lietz are Postdoctoral Researchers, and Markus Strohmaier is a Scientific Director at GESIS -Leibniz Institute for the Social Sciences.Address correspondence to Dr. Sebastian Stier, Department Computational Social Science, GESIS -Leibniz Institute for the Social Sciences, Unter Sachsenhausen 6-8, Köln, D-50667. E-mail: sebastian.stier@gesis.org Color versions of one or more of the figures in the article can be found online at www. tandfonline.com/UPCP. Political Communication, 35:50-74, 2018© 2017 Taylor & Francis Group, LLC ISSN: 1058 print / 1091-7675 online DOI: https://doi.org/10. 1080/10584609.2017.1334728 adapt the contents of their messages to the peculiarities of different platforms generates deeper insights into how political communication is shaped by social media.Much research revealed a continuation of the status quo in online campaigning, as politicians mostly replicated traditional messages and campaign mo...