Background: The questions and decisions involved in medical research are becoming increasingly complex and require more complex evaluation and synthesis of existing evidence. These require novel and sophisticated methodological approaches in synthesising different types of data, in evaluating multidisciplinary and complex interventions, and in synthesising appropriate data for further analysis, such as economic evaluations. In response to this, the National Institute for Health (NIHR) Research Complex Reviews Support Unit (NIHR CRSU) is a new initiative, funded by NIHR to support and encourage successful delivery of complex reviews of importance to the UK National Health Service (NHS), and to contribute to building capacity and capability within the research community. NIHR CRSU is led by the University of Glasgow, in collaboration with the University of Leicester and the London School of Hygiene and Tropical Medicine.

Objectives: The primary objective of the unit is to build a successful working relationship with NIHR in supporting the UK NHS in delivering clinically and cost-effective services that are evidence-based. The CRSU will focus on providing timely and appropriate support for the delivery of complex reviews that are funded and/or supported by NIHR. These include Cochrane Reviews, reviews funded by the Systematic Review Programme and other NIHR programmes, and other NHS and NHS supported sources. The unit will also work closely with NIHR to support scoping and prioritising of future complex reviews.

Methods: The collaboration of the three academic institutions forming NIHR CRSU, makes available a wide range of expertise in diagnostic test accuracy (DTA) reviews, network meta-analysis (NMA), individual participant data (IPD) meta-analysis, economic evaluation, realist synthesis, qualitative reviews, use of routine data, non-randomised studies, prognostic reviews, prevalence reviews and causal pathway analysis. Through a programme of workshops and ‘Seminars with cutting edge methods’, alongside direct support to individuals and groups, the CRSU will provide advice and support to unexpected challenges arising in complex reviews.