Animal Cognition

, Volume 14, Issue 4, pp 465–476 | Cite as

Decision-making under uncertainty: biases and Bayesians

  • Pete C. Trimmer
  • Alasdair I. Houston
  • James A. R. Marshall
  • Mike T. Mendl
  • Elizabeth S. Paul
  • John M. McNamara


Animals (including humans) often face circumstances in which the best choice of action is not certain. Environmental cues may be ambiguous, and choices may be risky. This paper reviews the theoretical side of decision-making under uncertainty, particularly with regard to unknown risk (ambiguity). We use simple models to show that, irrespective of pay-offs, whether it is optimal to bias probability estimates depends upon how those estimates have been generated. In particular, if estimates have been calculated in a Bayesian framework with a sensible prior, it is best to use unbiased estimates. We review the extent of evidence for and against viewing animals (including humans) as Bayesian decision-makers. We pay particular attention to the Ellsberg Paradox, a classic result from experimental economics, in which human subjects appear to deviate from optimal decision-making by demonstrating an apparent aversion to ambiguity in a choice between two options with equal expected rewards. The paradox initially seems to be an example where decision-making estimates are biased relative to the Bayesian optimum. We discuss the extent to which the Bayesian paradigm might be applied to the evolution of decision-makers and how the Ellsberg Paradox may, with a deeper understanding, be resolved.


Ambiguity Animal decisions Cognitive bias Ellsberg Paradox Risk Uncertainty 



PCT was supported by ERC grant 250209 Evomech.


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Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  • Pete C. Trimmer
    • 1
    • 2
  • Alasdair I. Houston
    • 2
  • James A. R. Marshall
    • 3
  • Mike T. Mendl
    • 4
  • Elizabeth S. Paul
    • 4
  • John M. McNamara
    • 5
  1. 1.Department of Computer ScienceUniversity of Bristol, Merchant Venturers BldgBristolUK
  2. 2.School of Biological SciencesUniversity of BristolBristolUK
  3. 3.Department of Computer Science / Kroto Research InstituteUniversity of SheffieldSheffieldUK
  4. 4.School of Veterinary ScienceUniversity of BristolBristolUK
  5. 5.School of MathematicsUniversity of BristolBristolUK

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