SHOULD THE SINGLE-BLIND PLACEBO RESPONDER EXCLUSION PHASE BE OMITTED FROM CLINICAL-TRIALS

A single-blind placebo responder exclusion phase is often included in clinical trials, to identify and exclude placebo responders. After classifying patients as placebo responders or placebo non-responders, only non-responders are included in the actual trial and randomized to active drug or placebo. The main purpose of this exclusion of responders is to make the sample of patients more homogeneous and thereby reduce the number of patients needed to draw a conclusion about the efficacy of the trial drug. Inclusion of placebo responders would also tend to reduce the difference between active drug and placebo and accordingly lead to an increase in the sample size necessary to obtain a certain power when performing a significance test. Several problems arise, however: 1) Do placebo responders exist? 2) Regression towards the mean. 3) Can trial results be generalized? With regard to the items listed above, the most natural answer to the question raised in the title is yes.