An introduction to Bayes' theorem and examples of its application to a diagnostic test and a clinical trial.

Background: The Bayesian approach to updating scientific knowledge involves using a probability distribution to describe a prior belief concerning an outcome of interest and combines this with some new information to create a posterior probability distribution to describe the updated current knowledge.

Aim: To introduce the application of Bayes' theorem, using the conditional probability example of the Monty Hall problem and two examples of the clinical application of a Bayesian approach.

Discussion: Bayesian approaches enable the incorporation of prior knowledge into the interpretation of research findings and summaries of evidence to date. Bayesian approaches are being incorporated into most clinical trials.

Conclusion: Bayesian approaches to interpreting the results of a diagnostic test and a clinical trial highlight the utility of these approaches to clinical nursing and the application of evidence-based practice.

Implications for practice: Stimulation of an understanding and interest in the Bayesian approach among nurse researchers should lead to its wider application in nursing research.