<p dir="ltr">Humans are social beings and throughout our evolution we have survived and thrived thanks to our ability to cooperate [7]. Overcoming our current societal challenges from sustainability and energy conservation [8] to democracy, public health, and community building [9] will all require our continued cooperation. Yet, many of these present us with a dilemma where our short-term personal goals are at odds with the collective long-term benefits. For example, many of us listen NPR radio but never make a donation to help cover its operational costs. The success of cooperation during such dilemmatic situations often depends on communication, reward and punishment structures, social norms and cues [10], [11], [12], [13]. But how to encourage cooperation online where social cues are not readily available?</p><p dir="ltr">Accelerated by the COVID-19 pandemic and the prevalence of digital technologies, cooperation among individuals increasingly happens online where data-based feedback supports our decisions. Problematically, people online are often not only remote and asynchronous, but often also anonymous, which has resulted in de-individuation and antinormative behavior [14]. Social data, information that users share about themselves via digital technologies, may offer opportunities for social feedback design that affords perceptions of social cohesion and may support successful cooperation online.</p><p dir="ltr">This dissertation seeks to answer the normative question of how to design for cooperation in social data feedback charts in dilemmatic situations online. I conducted mixed methods design research by combining theory-driven design with a series of controlled experiments on Amazon Mechanical Turk to understand the perceptual and behavioral effects of visually unifying social data feedback charts. To achieve this, I mapped the design space for home energy feedback (<i>Chapter 2</i>) to guide my iterative and user-centered theorizing about how visual unity in social feedback charts might prime viewers with unified group perceptions (<i>Chapter 3</i>). I then validated my theorizing with controlled perceptual (<i>Chapter 4</i>) and decision experiments (<i>Chapter 5</i>).</p><p dir="ltr">The triangulated results offer evidence for visually unifying cues in feedback charts affecting social data interpretation (<i>Chapter 4</i>) and cooperation online (<i>Chapter 5</i>). Two visual properties: data point <i>proximity</i> and <i>enclosure</i> -, trigger variable levels of perceivable social unity that play a partial role in participants’ decision to cooperate in a non-monetary social dilemma situation online. I discuss the implications for future research and design (<i>Chapter 6</i>).</p>