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Ellsberg Paradox

A precise number can make uncertainty easier to grasp while also concealing which parts of the probability model itself remain uncertain.

Ellsberg distinguishes risk with known probabilities from ambiguity about the probability model itself. A single persuasive AI probability estimate can obscure uncertainty across several plausible models.

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Research statusResearch in preparation
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AI relevanceAI may amplify an existing effect
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Core ideaAmbiguity / model uncertainty
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Evidence baseSources and limitations summarised; independent review pending.
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Case typeDecision-making paradox
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In one sentence

A precise number can make uncertainty easier to grasp while also concealing which parts of the probability model itself remain uncertain.

The storyHow the case arises and how it can mislead our thinking.

In Ellsberg’s famous urn choice problems, people often prefer a situation with known probabilities to one in which the distribution of colours is unknown, even when a single conventional subjective probability distribution struggles to explain the combination of choices.

What do we know?Evidence, research, critical insights and what remains unknown.

Ambiguity aversion is robust on average but not universal; ambiguity seeking also occurs, and behaviour varies with the source, probability and context. The case therefore does not support a general rule that ‘people avoid uncertainty’.

What is the mechanism?Which explanation best fits what we observe.

Uncertainty about the probabilistic model is itself relevant to decisions. Compressing this second-order uncertainty into a single probability may remove relevant epistemic structure.

What does AI change?How AI may amplify the mechanism or make it visible.

AI transfer to investigate: AI may change how uncertainty is represented by presenting advice as a single precise probability, a probability alongside confidence in the evidence, or several plausible models. The mechanism is old; the representation changes.

What do we want to test?The specific question we want to investigate further.

Proposed test, not yet conducted: Present identical ambiguous evidence under four conditions: no AI; one precise AI probability; probability plus confidence in the evidence/model; several plausible scenarios. Later add confirming or falsifying information and measure confidence, choice and updating.

What do we take away?What this case provisionally means — and where its limits lie.

The research aim is not less trust, but better-calibrated trust. Risk, ambiguity and model uncertainty should remain separately visible where relevant.

Updating a judgement after new information and calibration are different outcomes. Calibration compares stated probabilities with observed outcomes across suitable repeated tasks.

SourcesPrimary and key scholarly sources.

Ellsberg (1961), Risk, Ambiguity, and the Savage Axioms

Ellsberg (1961), full article

Ellsberg (1961, pp. 650–653 and 657–660) discusses urn choices and distinguishes probability judgements from confidence in them. His original response account was non-experimental. This discussion is not a comprehensive assessment of modern follow-up research or of the proposed AI test.

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