An overview of conducting systematic reviews with network meta-analysis

Introduction Systematic reviews with network meta-analysis (NMA) are published with increasing frequency in the health care literature. Prior to 2008, very few systematic reviews contained a NMA [1]; however, there has been a marked increase, to mid-2012 Lee recorded 201 published networks [2]. The statistical method has been available since 2002 [3,4] and owes its origins to much earlier work [5,6]. NMA has matured and models are available for all types of underlying data and summary effect measures [7-12] and can be readily implemented in both frequentist and Bayesian frameworks with pre-written programmes available in widely used softwares [8,13-15]. Recently, focus has shifted to making NMA more accessible [16,17]; however, the conduct of systematic reviews for NMA has received less attention [18]. In this special thematic series on network meta-analysis, the editors of Systematic Reviews are encouraging submissions of methodological papers concerning the conduct and reporting of meta-analyses and results papers (http://www. systematicreviewsjournal.com/about/update/SysRevCFP). As a preface to the series, this editorial provides an overview of the basic principles of NMA and summarises some of the key challenges for those conducting a systematic review.