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Sprint projectOct 25, 2026cape town

Parallel-Conduct-Is-Not-Agreement

Mufaro Rukuni · Team parallel com

Submitted to AI Collusion Research Sprint. Sprint projects are early-stage work by participants, not Apart Research publications.

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Mutual-information-style detectors ask whether two agents' actions are dependent. In a market they always are: every seller reacts to the same demand shock and to the same rival prices, so an auditor using dependence alone charges sellers with colluding for the crime of facing the same market. This project measures that failure (pricing_innocent_parallelism is flagged at a higher dependence level than either actual arrangement), builds a better instrument (the innocent null as a fitted reaction function rather than as a hypothesis of independence, plus localisation and conduct factors that survive it), and reports honestly what still cannot be detected: a market-wide agreement has no outsider to contrast against, and a deterministic convention leaves almost no residual dependence for any information-theoretic statistic to find.

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  1. Strong result on parallelism looking like a cartel and conventions being invisible under a pure matching metric. The point that static cartels leave no enforcement trace while rotations leave anti-correlated forbearance meaning that no single conjunction can catch both is also very interesting. However, this is arguably somewhat more relevant to the legal than the economic question: markup tests when feasible, or demand rotations when not, remain perfectly valid ways in such settings of identifying cartel-like behaviour regardless. The agreements also barely improve surplus in the setting.

Cite this project

@misc{rukuni2026parallelconductisnotagreement,
  title = {{Parallel-Conduct-Is-Not-Agreement}},
  author = {Mufaro Rukuni},
  year = {2026},
  month = oct,
  note = {Submitted to AI Collusion Research Sprint, an Apart Research Sprint},
  howpublished = {\url{https://apartresearch.com/sprints/projects/parallelconductisnotagreement-tw3u}},
  url = {https://apartresearch.com/sprints/projects/parallelconductisnotagreement-tw3u}
}

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