Comparing Two Groups or Treatments—A Bayesian Approach

The purpose of this paper is to illustrate the value of a Bayesian approach in practical problems involving two groups (treatments) which are to be compared. Using practical criteria for comparisons, the advantage of the Bayesian approach will be demonstrated in two situations. Problem I will deal with cholesterol data from two groups of people and it is the aim of the experiment to say which group has the higher cholesterol levels. Problem II will compare two treatments in a clinical trial situation at an interim before the trial is completed. This situation is referred to as interim analysis because only part of the data in the planned trial has been collected. At this interim stage it is desirable to decide whether to stop the experiment now or to continue until the end.