title: Meta-analysis, complexity, and heterogeneity: a qualitative interview study of researchers' methodological values and practices.
abstract: Complex or heterogeneous data pose challenges for systematic review and meta-analysis. In recent years, a number of new methods have been developed to meet these challenges. This qualitative interview study aimed to understand researchers' understanding of complexity and heterogeneity and the factors which may influence the choices researchers make in synthesising complex data.
  
  
  
  We conducted interviews with a purposive sample of researchers (N = 19) working in systematic review or meta-analysis across a range of disciplines. We analysed data thematically using a framework approach.
  
  
  
  Participants reported using a broader range of methods and data types in complex reviews than in traditional reviews. A range of techniques are used to explore heterogeneity, but there is some debate about their validity, particularly when applied post hoc.
  
  
  
  Technical considerations of how to synthesise complex evidence cannot be isolated from questions of the goals and contexts of research. However, decisions about how to analyse data appear to be made in a largely informal way, drawing on tacit expertise, and their relation to these broader questions remains unclear.
authors.affiliation: Centre for Reviews and Dissemination, University of York, York, YO10 5DD, UK. theo.lorenc@york.ac.uk.
authors.forename: Theo
authors.identifier: 0000-0001-8937-6378
authors.initials: T
authors.lastname: Lorenc
authors.affiliation: Department of Social and Environmental Health Research, London School of Hygiene & Tropical Medicine, 15-17 Tavistock Place, London, WC1H 9SH, UK.
authors.forename: Lambert
authors.initials: L
authors.lastname: Felix
authors.affiliation: Department of Social and Environmental Health Research, London School of Hygiene & Tropical Medicine, 15-17 Tavistock Place, London, WC1H 9SH, UK.
authors.forename: Mark
authors.initials: M
authors.lastname: Petticrew
authors.affiliation: Warwick Evidence, Division of Health Sciences, Coventry, CV4 7AL, UK.
authors.forename: G J
authors.initials: GJ
authors.lastname: Melendez-Torres
authors.affiliation: EPPI-Centre, Social Science Research Unit, UCL Institute of Education, 20 Bedford Way, London, WC1H 0AL, UK.
authors.forename: James
authors.initials: J
authors.lastname: Thomas
authors.affiliation: Department of Social and Environmental Health Research, London School of Hygiene & Tropical Medicine, 15-17 Tavistock Place, London, WC1H 9SH, UK.
authors.forename: Sian
authors.initials: S
authors.lastname: Thomas
authors.affiliation: EPPI-Centre, Social Science Research Unit, UCL Institute of Education, 20 Bedford Way, London, WC1H 0AL, UK.
authors.forename: Alison
authors.initials: A
authors.lastname: O'Mara-Eves
authors.affiliation: EPPI-Centre, Social Science Research Unit, UCL Institute of Education, 20 Bedford Way, London, WC1H 0AL, UK.
authors.forename: Michelle
authors.initials: M
authors.lastname: Richardson
mesh_terms: D035843:Biomedical Research; D003657:Decision Making; D007722:Health Knowledge, Attitudes, Practice; D006801:Humans; D015201:Meta-Analysis as Topic; D036301:Qualitative Research; D012107:Research Design; D012108:Research Personnel; D012196:Review Literature as Topic
keywords: Complexity; Heterogeneity; Meta-analysis; Qualitative research; Systematic review methodology