Indirect comparison refers to a comparison of different healthcare interventions using data from separate studies, and is often used because of a lack of, or insufficient evidence from head-to-head comparative trials. We aimed to summarize the definition, fundamental theory, type, relevant statistical contents, and to clarify some question on how to use indirect comparison, in order to attract more researchers' attention and promote methodological development of indirect comparison.
In 2014, the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) working group published guidance in BMJ to evaluate the certainty of the evidence (confidence in evidence, quality of evidence) from network meta-analysis. GRADE working group suggested rating the certainty of direct evidence, indirect evidence, and network evidence, respectively. Recently, GRADE working group has published a series of papers to improve and supplement this approach. This paper introduces the frontiers and advancement of GRADE approach to rate the certainty of evidence from network meta-analysis.