Project partners


  1. TrainBayes (DFG)
  2. siMINT (BMBF)
  3. FEHLBa (DFG)



  1. Material from the project TrainBayes (DFG)

Simulation with frequencies

Here, the frequencies of the different (sub)sets in a Bayesian situation are given in which 1000 people are tested with a medical diagnostic test. In the beginning it is assumed:
  • 8% of all people are ill.
  • 90% of the ill people are identified with the medical diagnostic test and hence test positive.
  • 15% of the healthy people are tested positive by mistake.

An interesting question in such a situation is: How likely is a person actually ill, if this person tests positive?
This probability is equivalent to the proportion of ill (and positively tested) people among all positively tested people. This proportion is represented in the fraction on the right-hand side and the frequencies are highlighted, which are necessary for the calculation.

The given information in the Bayesian situation can vary. Hence, the question arises, how variations of the three given pieces of information affect the probability that a person is actually ill, if this person tests positive.

With this simulation you can visualize and analyse the effects of such variations in the frequencies and the fraction, which represents the probability of interest.
Imagined sample: people
Attribute 1:
ill →
% of all people
healthy →
Attribute 2:
test positive →
test negative →
Combinations of the two attributes:
ill and test positive →
% of the ill people
ill and test negative →
healthy and test positive →
% of the healthy people
healthy and test negative →
= +