Background: This year (2019) marks the release of the sixth edition of the Cochrane Handbook for Systematic Reviews of Interventions. The first major update in a decade, this new edition includes new chapters and a fresh perspective on conducting systematic reviews as the questions and the evidence we consider become ever more complex. Over 100 authors and editors contributed to the new Handbook, updating everything from the core methods underpinning all reviews, from question formulation and data collection to advanced and specialized techniques. Both new and experienced contributors and users of Cochrane evidence are encouraged to review the updated guidance. 

Objectives: to provide an overview of the new Handbook, followed by presentations drawing on key new chapters, presented by their lead authors.

Description: in keeping with the themes of this Colloquium, this special session highlights advances in thinking around complexity and diversity of evidence introduced in this new Handbook, of particular relevance to complex questions around public health, health systems and consumer involvement in research. This enhanced guidance can be applied to the core methods of many reviews, tackling some of the most common difficulties faced by authors working with complex evidence, including multi-faceted questions that are of critical interest to healthcare and policy decision-makers. Complementing some of the more well-known additions to the Handbook, including the Risk of Bias 2 tool, ROBINS-I and network meta-analysis, these facets of complexity will support authors and editors in enhancing the conduct of a wide range of reviews as part of Cochrane’s broader efforts towards equity, diversity and relevance to decision makers.

Presentations by the Handbook's authors will include the following.
- Equity and specific populations (Vivien Welch) – building considerations of equity into question formulation and planning to enable effective investigation of the distribution of effects across populations and understanding of their impact on equity.
- Summarizing study characteristics and preparing for synthesis (Sue Brennan) – enabling clarity of understanding of the similarities and differences between the included studies, and defining in advance the categories and comparisons that will be used to analyse complex evidence.
- Intervention complexity (James Thomas) – addressing both multi-component interventions and interactions between interventions, their context and the system within which they are introduced.
- Synthesizing and presenting findings without meta-analysis (Jo McKenzie) – providing tools for authors to structure and interpret complex evidence when meta-analysis is not appropriate.