Network meta-analysis (NMA) is supposed to increase precision (because it includes more studies in the analysis); however, this is not always the case. This empirical study evaluated 915 possible treatment comparisons. The study used the recently proposed borrowing of strength statistic, which quantifies the percentage reduction in the uncertainty of the effect estimate when adding indirect evidence to an NMA
When only one study contributed direct evidence, NMAs resulted in reduced precision and no appreciable improvements in precision in 57.5% and 12.7% comparisons, respectively. When at least two studies contributed direct evidence, NMAs provided increased precision in 66.4% comparisons. The bottom-line is that, in sparse networks (i.e., networks that mostly consist of indirect evidence), NMA may not improve precision as much as stakeholders want and expect.
