We propose a technique we call piggyback prototyping, a prototyping mechanism for designing new social computing systems on top of existing ones. Traditional HCI prototyping techniques do not translate well to large social computing systems. To address this gap, we describe a 6-stage process for prototyping new social computing systems using existing online systems, such as Twitter or Facebook. This allows researchers to focus on what people do on their system rather than how to attract people to it. We illustrate this technique with an instantiation on Twitter to pair people who are different from each other in airports. Even though there were many missed meetings, 53% of survey respondents would be interested in being matched again, and eight people even met in person. Through piggyback prototyping, we gained insight into the future design of this system. We conclude the paper with considerations for privacy, consent, volume of users, and evaluation metrics.

The term email overload has two definitions: receiving a large volume of incoming email, and having emails of different status types (to do, to read, etc). Whittaker and Sidner proposed the latter definition in 1996, noticing that email inboxes were far more complex than simply containing incoming messages. Sixteen years after Whittaker and Sidner, we replicate and extend their work with a qualitative analysis of Google's Gmail. We find that email overload, both in terms of volume and of status, is still a problem today. Our contributions are 1) updating the state of email overload, 2) extending our understanding of overload in the context of Gmail and 3) comparing personal with work email accounts: while work email tends to be status overloaded, personal email is also type overloaded. These comparisons between work and personal email suggest new avenues for email research.

This paper presents a study of Nextdoor, a social media system designed to support local neighborhoods. While not the first system designed to support community engagement, Nextdoor has a number of attributes that make it distinct. Our study, across three communities in a major U.S. city, illustrates that Nextdoor inhabits an already-rich ecosystem of community-oriented social media, but is being appropriated by its users for use in different ways than these existing media. Nextdoor also raises tensions in how it defines the boundaries of neighborhoods, and in the privacy issues it raises among its users.

Most people associate with people like themselves, a process called homophily. Exposure to diversity, however, makes us more informed as individuals and as a society. In this paper, we investigate political disagreements on Facebook to explore the conditions under which diverse opinions can coexist online. Via a mixed methods approach comprising 103 survey responses and 13 interviews with politically engaged American social media users, we found that participants who perceived more differences with their friends engaged less on Facebook than those who perceived more homogeneity. Weak ties were particularly brittle to political disagreements, despite being the ties most likely to offer diversity. Finally, based on our findings we suggest potential design opportunities to bridge across ideological difference: 1) support exposure to weak ties; and 2) make common ground visible while friends converse.

As kids encounter food advertisements, it is important that they be able to critically evaluate the message's claims, the healthiness of the promoted product and their desire for it. To explore how technology might help kids develop these skills, we created an online forum called TalkBack that encourages children to critically analyze the messaging in food ads and their attitudes towards marketed foods. We evaluated TalkBack with twenty-eight middle school students in a summer camp program. We discuss how participants appeared to project and protect their sense of self through their interaction with TalkBack. We also describe the limited analytic depth of their forum contributions and suggest directions for HCI research that attempts to encourage critical thinking and health promotion in adolescents.

Eating with others, or commensality, is an enjoyable activity that serves many important social functions; however, many individuals eat meals alone due to life circumstances, meaning that they miss out on these social benefits. We developed and deployed a simple technology probe providing social awareness around mealtimes to explore how social systems might help alleviate the loneliness of solitary dining. Our findings suggest that these systems can convey a sense of connectedness around a meal; further, our analysis revealed three themes relevant to systems of this type: that contextually-located peripheral awareness engenders connectedness; that such tools can foster a feeling of shared social presence, and that they can be a catalyst for other forms of communication around the meal. These findings suggest that "remote commensality" is not only possible, but that it may take on forms entirely different to that which we are accustomed.

Collaborative tagging mechanisms are integral to social computing applications in a variety of domains. Their expected benefits include simplified retrieval of digital content, as well as enhanced ability of a community to makes sense of the shared content. We examine the impact of collaborative tagging in context of nutrition management. In a controlled experiment we asked individuals to assess the nutritional value of meals based on photographic images and observed the impact of different types of tags and tagging mechanisms on individuals nutritional sensemaking. The results of the study show that tags enhance individuals' ability to remember the viewed meals. However, we found that some types of tags can be detrimental to sensemaking, rather than supporting it. These findings stress the importance of tagging vocabularies and suggest a need for expert moderation of community sensemaking.

Molecular and computational biologists develop new insights by gathering heterogeneous data from genomic databases and leveraging bioinformatics tools. Through a qualitative study with 17 participants, we found that molecular and computational biologists experience difficulties interpreting, comparing, annotating, sharing, and relating this vast amount of biological information. We further observed that such interactions are critical for forming new scientific hypotheses. These observations motivated the creation of G-nome Surfer, a tabletop interface for collaborative exploration of genomic data that implements multi-touch and tangible interaction techniques. G-nome Surfer was developed in close collaboration with domain scientists and is aimed at lowering the threshold for using bioinformatics tools. A first-use study with 16 participants found that G-nome Surfer enables users to gain biological insights that are based on multiple forms of evidence with minimal overhead.