RCT

The cornerstone of clinical research on interventions is generally considered to be the randomized controlled trial (RCT). However, in topic areas where the number of patients is limited or the evidence is conflicting, systematic reviews offer the benefit of collating evidence from a variety of sources. A systematic review attempts to bring together all available evidence on a specific, clearly defined topic. Moreover, in areas where a number of large-scale trials have had similar results, a systematic review that includes meta-analysis of the data can help researchers to find a population estimate for the overall effect of the intervention.

In the hierarchy of evidence, systematic reviews of randomized trials offer the highest level of evidence. The strongest inferences can be drawn if the systematic review is well conducted and includes methodologically sound RCTs with consistent results. In making treatment decisions, the highest quality of evidence should be sought, but well-conducted systematic reviews may not always be available.

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4414076

cornerstone: a basic element

Meta-analysis is a research process used to systematically synthesize or merge the findings of single, independent studies, using statistical methods to calculate an overall or ‘absolute’ effect. Meta-analysis does not simply pool data from smaller studies to achieve a larger sample size. Analysts use well recognized, systematic methods to account for differences in sample size, variability (heterogeneity) in study approach and findings (treatment effects) and test how sensitive their results are to their own systematic review protocol (study selection and statistical analysis).

https://ebn.bmj.com/content/16/1/3