Few would argue that the randomized clinical trial is the most definitive instrument available for measuring the safety and efficacy of a new medical technology, be it drug, device, or procedure. Randomization removes the potential for bias in the allocation of subjects to the intervention group or to the control group. In addition, randomization tends to produce comparable groups which can be further strengthened by stratification and by stratified analyses. The randomized controlled trial guarantees validity of statistical tests, as long as the sample size is large enough to avoid type-II error.