What is the Ellsberg paradox (Ellsberg phenomenon)?

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Last updated: April 4, 2025View editorial policy

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From the Research

The Ellsberg paradox is a decision-making phenomenon where people prefer known risks over unknown risks, even when the unknown option might be more favorable, and this behavior is influenced by ambiguity aversion, which can be reduced but not abolished by learning about the paradox, as shown in a study published in 2020 1. The Ellsberg paradox demonstrates how people's decisions are influenced by ambiguity, which is the uncertainty or unknown probability of an outcome. This cognitive bias affects many real-world decisions, from financial investments to medical treatment choices, where people often choose familiar options with known risks over potentially better alternatives with uncertain probabilities.

  • The paradox reveals that people's decisions are influenced not just by risk (known probabilities) but also by ambiguity (unknown probabilities).
  • A study published in 2020 found that learning about the Ellsberg paradox can reduce ambiguity aversion, but it does not completely abolish it 1.
  • The study also found that participants who learned about the paradox exhibited reduced aversion to risk, suggesting that learning about the paradox can have a generalizing effect on decision-making under uncertainty.
  • Understanding the Ellsberg paradox can help explain seemingly irrational choices in uncertain situations and why people might avoid potentially beneficial options simply because the probabilities are unclear.
  • The paradox has implications for many fields, including finance, medicine, and psychology, where decision-making under uncertainty is a critical aspect of practice.
  • For example, in medicine, the Ellsberg paradox can influence treatment choices, where patients may prefer a treatment with known risks over a new treatment with uncertain probabilities, even if the new treatment has the potential to be more effective.
  • Therefore, it is essential to consider the Ellsberg paradox when making decisions under uncertainty, and to take steps to reduce ambiguity aversion, such as seeking out information and learning about the probabilities of different outcomes.

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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