The three large null experiments refute the ideological-diversity/echo-chamber pathway to algorithmic polarization but do not address the AAPA-amplification pathway identified by Piccardi et al. (2025), which remains supported by only one 10-day study on a single platform.

[NARROW-VARIANT] Guess et al. (2023) randomized 23,377 Facebook and Instagram users to chronological versus algorithmic feeds for three months during the 2020 election and found no effect on affective polarization. Nyhan et al. (2023) experimentally reduced exposure to like-minded sources on Facebook and found no reduction in affective polarization, ideological extremity, or candidate evaluations. Guess et al. (2023) on reshares similarly found that removing reshared political content from feeds did not affect polarization outcomes. Therefore (narrowed), The three large null experiments refute the ideological-diversity/echo-chamber pathway to algorithmic polarization but do not address the AAPA-amplification pathway identified by Piccardi et al. (2025), which remains supported by only one 10-day study on a single platform.

• Guess et al. (2023) randomized 23,377 Facebook and Instagram users to chronological versus algorithmic feeds for three months during the 2020 election and found no effect on affective polarization.
• Nyhan et al. (2023) experimentally reduced exposure to like-minded sources on Facebook and found no reduction in affective polarization, ideological extremity, or candidate evaluations.
• Guess et al. (2023) on reshares similarly found that removing reshared political content from feeds did not affect polarization outcomes.

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• Is the absence of positive evidence strong enough to justify concluding ¬A, or only to justify withholding belief in A?Open
• Is the absence of evidence due to absence of investigation rather than to A's being false?Open
• Could disconfirming or null findings have been suppressed, unpublished, or systematically under-reported (file-drawer / publication bias)?Open
• Has the investigative regime actually been adequate (well-funded, well-powered, well-designed) to detect E if A were true?Open
• Could A be true but produce only a weak signal that escapes detection at the prevailing statistical thresholds?Open

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