title: Considering methodological options for reviews of theory: illustrated by a review of theories linking income and health.
abstract: BACKGROUND
  Review of theory is an area of growing methodological advancement. Theoretical reviews are particularly useful where the literature is complex, multi-discipline, or contested. It has been suggested that adopting methods from systematic reviews may help address these challenges. However, the methodological approaches to reviews of theory, including the degree to which systematic review methods can be incorporated, have received little discussion in the literature. We recently employed systematic review methods in a review of theories about the causal relationship between income and health.
  
  
  METHODS
  This article discusses some of the methodological issues we considered in developing the review and offers lessons learnt from our experiences. It examines the stages of a systematic review in relation to how they could be adapted for a review of theory. The issues arising and the approaches taken in the review of theories in income and health are considered, drawing on the approaches of other reviews of theory.
  
  
  RESULTS
  Different approaches to searching were required, including electronic and manual searches, and electronic citation tracking to follow the development of theories. Determining inclusion criteria was an iterative process to ensure that inclusion criteria were specific enough to make the review practical and focused, but not so narrow that key literature was excluded. Involving subject specialists was valuable in the literature searches to ensure principal papers were identified and during the inductive approaches used in synthesis of theories to provide detailed understanding of how theories related to another. Reviews of theory are likely to involve iterations and inductive processes throughout, and some of the concepts and techniques that have been developed for qualitative evidence synthesis can be usefully translated to theoretical reviews of this kind.
  
  
  CONCLUSIONS
  It may be useful at the outset of a review of theory to consider whether the key aim of the review is to scope out theories relating to a particular issue; to conduct in-depth analysis of key theoretical works with the aim of developing new, overarching theories and interpretations; or to combine both these processes in the review. This can help decide the most appropriate methodological approach to take at particular stages of the review.
authors.affiliation: MRC/CSO Social and Public Health Sciences Unit, University of Glasgow, Glasgow, UK. Mhairi.Campbell@glasgow.ac.uk.
authors.forename: Mhairi
authors.initials: M
authors.lastname: Campbell
authors.forename: Matt
authors.initials: M
authors.lastname: Egan
authors.forename: Theo
authors.initials: T
authors.lastname: Lorenc
authors.forename: Lyndal
authors.initials: L
authors.lastname: Bond
authors.forename: Frank
authors.initials: F
authors.lastname: Popham
authors.forename: Candida
authors.initials: C
authors.lastname: Fenton
authors.forename: Michaela
authors.initials: M
authors.lastname: Benzeval
mesh_terms: D016206:Databases, Bibliographic; D006304:Health Status; D006801:Humans; D007182:Income; D016247:Information Storage and Retrieval / Q000379:methods*; D008962:Models, Theoretical; D012107:Research Design; D012196:Review Literature as Topic