Overlapping network meta-analyses on the same topic: survey of published studies

Background
To assess how common it is for a published network meta-analysis (NMA) to have other published overlapping NMAs, and to evaluate these overlaps.

Methods
A total of 88 NMAs of randomized controlled trials evaluating the comparative effectiveness of health interventions were randomly selected. For each of these, we searched for NMAs on the same topic. A random sample of 40 pairs (an index NMA and one of its overlapping NMAs) was selected to assess the overlap in terms of nodes, treatments and references. The topic with the largest number of overlapping NMAs was described in depth.

Results
In all, 68 of the 88 index NMAs had at least one overlapping NMA: 77% [95% confidence interval (CI), 69–86%]. We identified 515 pairs of overlapping NMAs. Among the 40 randomly selected pairs, 73% (95% CI, 58–88%) of nodes, 79% (95% CI, 72–86%) of treatments and 48% (95% CI, 37–59%) of references included in the index NMAs were also found in the respective overlapping NMAs. Efficacy of biologics in rheumatoid arthritis had the largest number of overlapping NMAs, with 28 NMAs published between 2003 and 2014. Differences in selection and definition of nodes of treatments resulted in different network geometries. There were also differences in both the direction and the statistical significance of effects.

Conclusions
Published NMAs exhibit extensive overlap and potential redundancy. Erratic retrieval of eligible trials, and lack of consensus on the range of interventions to be considered and how they might be merged or split in different nodes, may cause confusion.