A Controlled Clinical Trial is the formal experimental approach to treatment evaluation. In such a trial, the investigator controls the assignment of treatments—ideally by randomization— to experimental groups. When well executed, such a trial provides the strongest evidence for the relative effectiveness of the different therapeutic interventions. Some people, myself among them, believe that the clinical trial approach should be used early when a new therapeutic modality is first introduced.

The purpose of a controlled clinical trial is to answer the question of whether the new therapy is preferable to standard therapies. If no standard therapy exists, then new therapy has to compete either with no treatment or placebo.