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YouTube Video Recommendations Lead to More Extremist Content for Right-Leaning Users, Researchers Suggest
(lettersandscience.ucdavis.edu)
This is a most excellent place for technology news and articles.
Even before signing in YouTube well still try to recommend what the overall household watches by matching it up to the IP address. It's also why when signing in you sometimes get recommended what someone else in your family watches even if you don't. Same thing happens when you're not signed in too.