Document Type : Review Article



In a number of important clinical issues such as evaluation of the efficacy or effectiveness of therapeutic or preventive interventions as well as for comparing the harms of interventions, randomized controlled trials (RCTs) provide the highest levels of evidence, either directly or indirectly. It is obvious that critical appraisal of these studies to assess their validity and precision is of paramount importance. The aim of this review is to provide the readership an outline about different types of RCTs, the importance of proper appraisal of RCTs, an overview of the most important factors that have an influence on the validity of an RCT and a strategy for systematic evaluation of those factors, and to introduce some useful methods for improving design, implementation and reporting of RCTs as well as some tools that are used for the evaluation of these studies. It is expected that after reading this review, the reader obtains some knowledge about different phases and types of RCTs, as well as being enabled to evaluate the four major factors: randomization sequence generation, randomization concealment, blinding and intention to treat analysis that affect the validity of an RCT.