Behavioral and Brain Sciences

Open Peer Commentary

The underinformative formulation of conditional probability

Laura Macchia1 and Maria Bagassia1

a1 Department of Psychology, University of Milano-Bicocca, 20126 Milan, Italy.


The formulation of the conditional probability in classical tasks does not guarantee the effective transmission of the independence of the hit rate from the base rate. In these kinds of tasks, data are all available, but subjects are able to understand them in the specific meanings proper to a specialized language only if these are adequately transmitted. From this perspective, the partitive formulation should not be considered a facilitation, but rather, a way of effectively transmitting the conditional probability.

Consider the following two phrases:

  • 1 The death-rate among men is twice that for women.
  • 2 In the deaths registered last month there were twice as many men as women.
Are these two different ways of saying the same or are these different events? In fact, they are different events. (Lindley 1985, p. 44)

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