Causally estimating the effect of YouTube's recommender system using counterfactual bots

TL;DR

This paper introduces 'counterfactual bots' to causally evaluate YouTube's recommender system, revealing that recommendations tend to moderate partisan content consumption rather than amplify it, especially after 2019 algorithm changes.

Contribution

The study presents a novel counterfactual bot methodology to isolate the causal impact of YouTube's recommendations on content partisan bias.

Findings

Recommenders lead to less partisan consumption on average.

Partisan preferences fade within 30 videos when switching to moderate content.

Post-2019 algorithm changes, individual preferences dominate content consumption.

Abstract

In recent years, critics of online platforms have raised concerns about the ability of recommendation algorithms to amplify problematic content, with potentially radicalizing consequences. However, attempts to evaluate the effect of recommenders have suffered from a lack of appropriate counterfactuals -- what a user would have viewed in the absence of algorithmic recommendations -- and hence cannot disentangle the effects of the algorithm from a user's intentions. Here we propose a method that we call ``counterfactual bots'' to causally estimate the role of algorithmic recommendations on the consumption of highly partisan content. By comparing bots that replicate real users' consumption patterns with ``counterfactual'' bots that follow rule-based trajectories, we show that, on average, relying exclusively on the recommender results in less partisan consumption, where the effect is most pronounced for heavy partisan consumers. Following a similar method, we also show that if partisan consumers switch to moderate content, YouTube's sidebar recommender ``forgets'' their partisan preference within roughly 30 videos regardless of their prior history, while homepage recommendations shift more gradually towards moderate content. Overall, our findings indicate that, at least since the algorithm changes that YouTube implemented in 2019, individual consumption patterns mostly reflect individual preferences, where algorithmic recommendations play, if anything, a moderating role.