Credits to
Susanna Arcieri

Brain, intuition and probability

First part. The hypothesis of Kahneman and Tversky and subsequent confirmations

Issue 4/2019


Eliminato l’impossibile, ciò che resta, per improbabile che sia,
deve essere la verità.
Sherlock Holmes[1]

Abstract. Statistical data e probabilistic calculations are frequently of great importance in criminal trials both during the probative examination and in the grounds for the ruling, following the outcome of the judgement. However, reasoning on the existence of a certain probability, affirming it or denying it, presupposes, obviously, an adequate understanding, at least, of the fundamental principles underlying probabilistic reasoning, both on the part of those who bring the statistical data into the process (the parties, the technical consultants and the experts) and of those who are called upon to evaluate the data (the judge). Therefore, from this point of view, it seems particularly interesting that that line of studies, developed in the field of psychology which, since the 1950s, has progressively gathered evidence according to which the human mind would, by nature, not be suitable for reasoning in terms of probability and to make statistical estimates. With the intention of providing an initial overview of the problem, this contribution focuses on some of the main acquisitions of the last ninety years in the context of the aforementioned research, with particular attention to the fundamental contribution of the discoveries made since the 1970s by the Israeli psychologists Amos Trevsky and Daniel Kahneman – winner of the 2002 Nobel Prize for Economics – in terms of  cognitive bias and relations between intuitive and rational thinking as part of the decision-making process.


SUMMARY: 1. Brains unable to do statistical calculations. – 2. The first source of error. Cause versus case. – 3. The second source of error: the application error. The rule of conjunction. – 4. (Continued) The so-called “player’s fallacy.” – 5. (Continued) The bias of the law of small numbers. – 6. Why are we doing it wrong? – 7. The limits of human rationality according to economic science. – 8. Further confirmation of the hypothesis of Kahneman and colleagues.


To read the Reflection, click on “open file”.


[1] A.C. Doyle, Il segno dei quattro, in Id., Tutto Sherlock Holmes, Vol. I, Newton Compton, 1993, p. 158.



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