Probability judgments may have to be revised if new information is available. From the mathematical perspective probability revisions are intimately connected to the notion of conditional probability and Bayes' formula, a subsidiary concept and a trivial theorem respectively. Nevertheless empirical investigations in subjects' understanding of probability do indicate that people do not cope adequately with situations involving probability revisions, if they have been taught the mathematical concepts or not does not matter. In what follows I will try to sketch some phenomena of misunderstanding, give some comments on the interplay between mathematics and intuitions which I think represents the origin of lack of comprehension. A brief overview on the favor concept should enable the impression that by way of teaching this concept probabilistic reasoning could be improved.
The CAUSE Research Group is supported in part by a member initiative grant from the American Statistical Association’s Section on Statistics and Data Science Education