The findings of the head-to-head trial of A and C, and of a second head-to-head trial of B and C, can be used to compare interventions A and B with each other indirectly. Part (a) of the Figure shows the simplest case of a network with three interventions, A, B, and C. a placebo) have been conducted, the method of adjusted indirect comparison as described by Bucher et al. If there is no evidence available from head-to-head trials comparing two interventions, but trials comparing each of the interventions of interest with the same comparator (e.g. This article therefore describes only procedures for adjusted indirect comparisons which further analyze, for example, the effects estimated in the trials. The general scientific consensus is that it is inappropriate to use nonadjusted indirect comparisons in which findings from individual arms of different trials are naively compared with each other without taking randomization into account ( 11, 12). This article aims to describe the underlying assumptions and methods used in indirect comparisons and network meta-analyses and to explain what evaluation of such publications should include. In addition to the well-known PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) statement ( 7, 8), a guideline has also been compiled for the publication of systematic reviews incorporating network meta-analyses ( 9). Since 2009, indirect comparisons and network analyses have become increasingly important ( 6). Cases such as these require procedures for indirect comparison or network meta-analysis. Rather than using numerous separate pairwise comparisons, it is preferable to perform a combined data analysis ( 5). Here, 14 interventions can be compared with each other. Another example is the research of various prostaglandins to induce labor. For comparison of newer anticoagulants in patients with atrial fibrillation, for example, although there are trials directly comparing each of the newer drugs with the current standard treatment (warfarin), there are none that compare two of the newer anticoagulants with each other directly ( 4). However, this approach becomes problematic when there are no head-to-head trials comparing the two interventions, or when more than two interventions need to be compared with each other simultaneously. To compare exactly two interventions, the results of available head-to-head trials (often randomized controlled trials) are quantitatively summarized in a meta-analysis ( 1– 3). Reviews are often used in medical research to collate, evaluate, and summarize the evidence on a particular clinical question systematically and transparently ( 1).
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