Treatment evaluation is one of the most important tasks in medical research. Detailed standards have been developed during the last decades. The efficacy/effectiveness of treatments can only be assessed in comparison to control groups. To guarantee the internal validity of these comparisons, the groups have to be comparable at the beginning of the study. This can be achieved by randomized allocation of patients to treatment. Furthermore, as far as possible patient and physician should be blinded to treatment in order to avoid subjective influences on treatment results. Groups should still be comparable when analysing the trial, thus an analysis according to the principle of intention-to-treat ("as randomized") should be performed. These indispensable principles for design, conduct and analysis of clinical trials are widely accepted and contribute to reliable and credible results.