Boxell et al.'s acknowledgment of theoretical spillover channels does not provide evidence that spillovers from young social media users to elderly non-users occurred at sufficient magnitude to account for the observed demographic pattern.

[DEFENSE-UNDERCUT → w4pchn] Boxell et al. (2017) acknowledge spillover channels as a theoretical possibility but present the demographic pattern as evidence arguing against internet-driven polarization. Boxell et al. (2024) conclude that US polarization trends are most consistent with US-specific factors like changing party composition, racial divisions, and partisan cable news. Boxell (2020) finds demographic change explains only 34% of polarization index change, but the remaining 66% encompasses all non-demographic factors including cable TV and elite polarization, not specifically algorithmic effects. Therefore, Boxell et al.'s acknowledgment of theoretical spillover channels does not provide evidence that spillovers from young social media users to elderly non-users occurred at sufficient magnitude to account for the observed demographic pattern. (Warrant: Acknowledging a theoretical spillover channel does not establish its magnitude; the authors themselves interpret the demographic pattern as evidence against internet-driven polarization, and the unexplained variance encompasses many non-algorithmic factors.)

• Boxell et al. (2017) acknowledge spillover channels as a theoretical possibility but present the demographic pattern as evidence arguing against internet-driven polarization.
• Boxell et al. (2024) conclude that US polarization trends are most consistent with US-specific factors like changing party composition, racial divisions, and partisan cable news.
• Boxell (2020) finds demographic change explains only 34% of polarization index change, but the remaining 66% encompasses all non-demographic factors including cable TV and elite polarization, not specifically algorithmic effects.

These are challenges this argument’s reasoning pattern must still withstand. Answering them on Isonomia strengthens the argument.

• Is there a plausible alternative hypothesis that has not been considered or that would explain the facts at least as well?Open
• Could the facts be jointly explained by a conjunction of weaker causes rather than a single dominant H?Open
• Could the body of facts F itself be an artifact of selection, measurement, or reporting bias rather than a real phenomenon needing causal explanation?Open
• Does H actually explain the full body of facts F, or only a salient subset?Open
• Are the criteria used to judge H 'best' (scope, simplicity, mechanism, prior probability) appropriate for this domain, and are they applied consistently across the alternatives?Open

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