Randomized, Controlled Trials, Observational Studies, and the Hierarchy of Research Designs

Randomized, controlled trials were introduced into clinical medicine when streptomycin was evaluated in the treatment of tuberculosis 1 and have become the gold standard for assessing the effectiveness of therapeutic agents. 2 – 4 The ascendancy of randomized, controlled trials was hastened by a landmark article 5 comparing published randomized, controlled studies with those that used observational designs. That review of the literature identified six different therapies evaluated in both randomized, controlled trials (50 studies) and trials with historical controls (56 studies). For each study, subjects in the treatment group were found to have similar rates of the outcome in question regardless of study . . .