title: Synthesizing evidence on complex interventions: how meta-analytical, qualitative, and mixed-method approaches can contribute.
abstract: OBJECTIVE
  Although there is increasing interest in the evaluation of complex interventions, there is little guidance on how evidence from complex interventions may be reviewed and synthesized, and the relevance of the plethora of evidence synthesis methods to complexity is unclear. This article aims to explore how different meta-analytical approaches can be used to examine aspects of complexity; describe the contribution of various narrative, tabular, and graphical approaches to synthesis; and give an overview of the potential choice of selected qualitative and mixed-method evidence synthesis approaches.
  
  
  METHODS
  The methodological discussions presented here build on a 2-day workshop held in Montebello, Canada, in January 2012, involving methodological experts from the Campbell and Cochrane Collaborations and from other international review centers (Anderson L, Petticrew M, Chandler J, et al.
  
  
  BACKGROUND
  systematic reviews of complex interventions. In press). These systematic review methodologists discussed the broad range of existing methods and considered the relevance of these methods to reviews of complex interventions.
  
  
  RESULTS
  The evidence from primary studies of complex interventions may be qualitative or quantitative. There is a wide range of methodological options for reviewing and presenting this evidence. Specific contributions of statistical approaches include the use of meta-analysis, meta-regression, and Bayesian methods, whereas narrative summary approaches provide valuable precursors or alternatives to these. Qualitative and mixed-method approaches include thematic synthesis, framework synthesis, and realist synthesis. A suitable combination of these approaches allows synthesis of evidence for understanding complex interventions.
  
  
  CONCLUSIONS
  Reviewers need to consider which aspects of complex interventions should be a focus of their review and what types of quantitative and/or qualitative studies they will be including, and this will inform their choice of review methods. These may range from standard meta-analysis through to more complex mixed-method synthesis and synthesis approaches that incorporate theory and/or user's perspectives.
authors: Social and Environmental Health Research Department, Faculty of Public Health and Policy, London School of Hygiene and Tropical Medicine, London WC1H 9SH, UK. Electronic address: Mark.Petticrew@lshtm.ac.uk.
authors: Mark
authors: M
authors: Petticrew
authors: Eva
authors: E
authors: Rehfuess
authors: Jane
authors: J
authors: Noyes
authors: Julian P T
authors: JP
authors: Higgins
authors: Alain
authors: A
authors: Mayhew
authors: Tomas
authors: T
authors: Pantoja
authors: Ian
authors: I
authors: Shemilt
authors: Amanda
authors: A
authors: Sowden
mesh_terms: D003627:Data Interpretation, Statistical; D006801:Humans; D012107:Research Design; D012196:Review Literature as Topic
keywords: Complex interventions; Evaluation; Evidence synthesis; Meta-analysis; Mixed methods; Systematic review