Overview of the Randomized Clinical Trial and the Parallel Group Design

Abstract

The randomized clinical trial (RCT) is considered to be the gold standard for determining whether a therapeutic intervention is effective in treating the specific medical condition of interest. The advent of the RCT is relatively recent, with the first major trial reporting results shortly after World War II. However, the various design elements that provide the rigor of the RCT had developed over hundreds of years. In fact, the basic idea of learning from comparison existed long before the advent of the scientific method and the subsequent development of the RCT.

While randomization is a key component of the method, a poorly designed (despite randomization) and conducted trial can negate the benefits of randomization. Thus, blinding of the treatment assignment when possible, maintaining high follow-up rates for those randomized, adherence to the study protocol and attention to high data quality help preserve the benefit of randomization.

There are three factors that need to be considered when designing a trial. The first is the principle of equipoise, which essentially means that there is enough knowledge of the potential effectiveness of an experimental treatment to warrant further study, but there remains sufficient doubt how the experimental treatment compares to an existing control (whether it is the current standard of care, placebo, or no intervention) to justify the trial. In fact, equipoise justifies randomization. The second is that the overall choice of treatments, assessments and other facets of the study design must adhere to ethical principles for human research. Finally, the trial must be feasible and have a reasonable expectation of successful completion.