Political content and news are polarized but other content is not in YouTube watch histories

Research on ideological biases and polarization on social media platforms primarilyfocuses on news and political content. Non-political content, which isvastly more popular, is often overlooked. Because partisanship is correlatedwith citizens’ non-political attitudes and non-political content can carry politicalcues, we explore whether ideological biases and partisan segregation extendto users’ non-political exposures online. We focus on YouTube, one of the mostpopular platforms. We rely online data from American adults (N = 2,237).From over 129 million visits to over 37 million URLs, we analyze 1,037,392visits to YouTube videos from 1,874 participants. We identify YouTube channelsof 942 news domains, utilize a BERT-based classifier to identify politicalvideos outside news channels, and estimate the ideology of all the videos inour data. We compare ideological biases in exposure to (a) news, (b) political,and (c) non-political content. We examine both exposure congeniality (i.e., areusers consuming like-minded content?) and polarization (i.e. are there overlapsbetween Democrats and Republicans in the content they consume?). Wefind substantial congeniality in the consumption of news and political videos,especially among Republicans, and high levels of polarization in this exposure(i.e., limited overlaps between Democrats and Republicans). We also showthat both exposure congeniality and polarization are significantly lower fornon-political content, in that non-political videos are less likely to be ideologicallylike-minded and both Democrats and Republicans consume similarnon-political content. Theoretical and practical implications of these findingsare discussed.