  In October 2017 the Italian National Institute of Statistics (ISTAT), Italy's
body for official statistics, has published the book of fairy tales Le streghe
di Bayes (The witches of Bayes) written by ISTAT staff members with the
commendable aim of introducing statistical and probabilistic reasoning to
children. In this paper the fairy tale which gives the name to the book is
analyzed in a dialog between three teachers with different background and
expertise. The outcomes are definitively discouraging, especially when the
story is compared to the appendix of the book, in which the teaching power of
every story is indeed explained (as a matter of fact, without the appendix the
fairy tale of the witches seemed to be written with the purpose of make the
'Bayesians', meant as the villagers from 'Bayes', ridiculous). In fact the
fairy tale of the witches does not contain any Bayesian reasoning, the
suggested decision strategy is simply wrong and the story does not even seem to
be easily modifiable (besides the trivial correction of the decision strategy)
in order to make it usable as a teaching tool. As it happens in real dialogues,
besides the fairy tale in question, the dialogue touches several issues somehow
related to the story and concerning probability, inference, prediction and
decision making. The present paper is an indirect response to the invitation by
the ISBA bulletin to comment on the fairy tale.
