Background:
The majority of network meta-analyses published to date have incorporated data from randomized controlled trials (RCTs) only, however, more and more network meta-analyses of treatment interventions include non-randomized trials (NRSs). NRSs can complement RCTs or address some of their limitations, especially in case of chronic diseases and when evidence from randomized trials is insufficient or lacking. Inclusion of both RCTs and NRSs in network meta-analysis will likely increase in the future due to the growing need to assess multiple treatments simultaneously, the availability of higher quality non-randomized data, and more valid methods. However, the methods of synthesizing results of both RCTs and NRSs in network meta-analyses are unclear.

Objectives:
The objectives of this presentation are to review the methods for dealing with results when the network meta-analysis includes RCTs and NRSs at the same time, and the impact that including NRSs in network meta-analysis will have on the results.

Methods:
We conducted a comprehensive literature search in PubMed from inception to January 2018. We included network meta-analyses of both RCTs and NRSs that provided sufficient data. We evaluated existing methodologies for using non-randomized evidence in a network meta-analysis of RCTs when the aim is to assess relative treatment effects, and calculated the impact that including NRSs in network meta-analysis makes on the results when the network meta-analysis includes both RCTs and NRSs.

Results and conclusions:
This study is ongoing and available results will be presented at the Cochrane Colloquium.

Patient or healthcare consumer involvement:
None.