Thomas Bayes (1701–1761) founded the Bayesian approach, published as “Essay Towards Solving a Problem in the Doctrine of Chances” in 1763 as a new philosophy in inferential statistics opposed to the classical, frequentist approach. Frequentists test whether a hypothesis is true or false with a certain probability. The Bayesian approach depends on conditional probability which takes prior knowledge (a prior distribution of probabilities) into account. An example for the use of the Bayesian approach is a self-reported instrument that assesses function in rheumatic and musculoskeletal diseases. This instrument produces worse scores with higher age due to the increasing incidence of physical disability. The prior knowledge (higher age leading to a worse function score) should be taken into account when the scores of the instruments are interpreted.

Disclosure of Interest None declared