Societal change is often driven by shifts in public opinion. As citizens evolve in their norms, beliefs, and values, public policies change too. While traditional opinion polling and surveys can outline the broad strokes of whether public opinion on a particular topic is changing, they usually cannot capture the full multi-dimensional richness and diversity of opinion present in a large heterogeneous population. However, an increasing fraction of public discourse about public policy issues is now occurring on online platforms, which presents an opportunity to measure public opinion change at a qualitatively different scale of resolution and context. In this paper, we present a conceptual model of observed opinion change on online platforms and apply it to study public discourse on Universal Basic Income (UBI) on Reddit throughout its history. UBI is a periodic, no-strings-attached cash payment given to every citizen of a population. We study UBI as it is a clearly-defined policy proposal that has recently experienced a surge of interest through trends like automation and events like the COVID-19 pandemic. We find that overall stance towards UBI on Reddit significantly declined until mid-2019, when this historical trend suddenly reversed and Reddit became substantially more supportive. Using our model, we find the most significant drivers of this overall stance change were shifts within different user cohorts, within communities that represented similar affluence levels, and within communities that represented similar partisan leanings. Our method identifies nuanced social drivers of opinion change in the large-scale public discourse that now regularly occurs online, and could be applied to a broad set of other important issues and policies.

翻译：社会变革往往由公众舆论的转变驱动。随着公民在规范、信仰和价值观上的演变，公共政策也随之变化。传统的民意调查和问卷调查虽能勾勒出公众对某一话题态度变化的宏观轮廓，但通常无法捕捉大规模异质人群中存在的多维丰富性和多样性。然而，如今关于公共政策议题的公众话语越来越多地发生在在线平台上，这为我们提供了在定性不同规模和语境下衡量公众舆论变化的机会。本文提出了一种观察在线平台中舆论变化的概念模型，并将其应用于研究Reddit上关于全民基本收入（UBI）的整个历史时期的公众话语。UBI是一种定期、无条件向每位公民发放的现金补贴。我们选择研究UBI，因为它是一个定义明确的政策提案，近年来因自动化和新冠疫情等事件而引发了兴趣激增。我们发现，Reddit上对UBI的整体态度在2019年中期之前显著下降，但此后这一历史趋势突然逆转，Reddit变得更为支持。利用我们的模型，我们发现，这种整体态度变化的最显著驱动力来自不同用户群体内部、代表相似富裕水平的社群内部，以及代表相似党派倾向的社群内部的态度转变。我们的方法在如今定期发生的大规模在线公共话语中识别出了舆论变化的微妙社会驱动力，并可广泛应用于其他重要议题和政策。