Multiple treatment meta-analyses are particularly suited to problems addressed by Overviews of reviews (Chapter 22). A particular advantage of using a Bayesian framework is that all interventions in the analysis can be ranked, using probabilistic, rather than crude, methods. Standard subgroup analysis and meta-regression methods can no longer be used, although the analysis can be performed in a Bayesian framework using WinBUGS: see Section 16.8.1. When some studies include more than two intervention groups, the synthesis requires multivariate meta-analysis methods. However, it is preferable to use a random-effects model to allow for heterogeneity within each subgroup, and this can be achieved by using meta-regression instead (see Chapter 9, Section 9.6.4). If each study compares exactly two interventions, then multiple-treatments meta-analysis can be performed using subgroup analyses, and the test for subgroup differences used as described in Chapter 9 (Section 9.6.3.1). If there are more than three interventions, then there will be several direct and indirect comparisons, and it will be more convenient to analyse them simultaneously. For example, if there are also trials of the direct comparison ‘doctor versus nurse’, then these might be combined with the results of the indirect comparison. This analysis may be extended in various ways. For example, doctors and nurses can be compared indirectly by contrasting trials of ‘dietician versus doctor’ with trials of ‘dietician versus nurse’. advice from dietician, advice from doctor, advice from nurse), any two can be compared indirectly through comparisons with the third.
The simplest example of a multiple-treatments meta-analysis is the indirect comparison described in Section 16.6.2.
This is in contrast to the methods for dealing with a single study with multiple intervention groups that are described in Section 16.5, which focus on reducing the multiple groups to a single pair-wise comparison. Note that multiple-treatments meta-analyses retain the identity of each intervention, allowing multiple intervention comparisons to be made. provide a readable introduction (Caldwell 2005) a more comprehensive discussion is provided by Salanti et al. Multiple-treatments meta-analyses can be used to analyse studies with multiple intervention groups, and to synthesize studies making different comparisons of interventions. These are usually referred to as ‘multiple-treatments meta-analysis’ (‘MTM’), ‘network meta-analysis’, or ‘mixed treatment comparisons’ (‘MTC’) meta-analysis. Methods are available for analysing, simultaneously, three or more different interventions in one meta-analysis. For the current version, please go to /handbook/current.
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