Considering methodological options for reviews of theory: illustrated by a review of theories linking income and health

Campbell et al. Systematic Reviews 2014, 3:114 http://www.systematicreviewsjournal.com/content/3/1/114 METHODOLOGY Open Access Considering methodological options for reviews of theory: illustrated by a review of theories linking income and health Mhairi Campbell1*, Matt Egan2, Theo Lorenc3, Lyndal Bond4, Frank Popham1, Candida Fenton1 and Michaela Benzeval1,5 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. Keywords: Review, Theory, Systematic review * Correspondence: 1 MRC/CSO Social and Public Health Sciences Unit, University of Glasgow, Glasgow, UK Full list of author information is available at the end of the article © 2014 Campbell et al.; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Campbell et al. Systematic Reviews 2014, 3:114 http://www.systematicreviewsjournal.com/content/3/1/114 Background Theory is fundamental to research and rational thought. The term ‘theory’ has been variously defined, and is frequently used without definition, but often refers to an explanatory framework for observations. In science, theories generally purport to explain empirical observations and form the basis on which testable hypotheses are generated to provide support for, or challenge, the theory. Gorelick defines theory as ‘the creative, inductive, and synthetic discipline of forming hypotheses’ [1], p. 7. Popper defined a scientific theory as one that is experimentally falsifiable [2]. Merton has contrasted ‘grand’ social theories such as Marxism, functionalism, and post-modernism with ‘middle-range theories’ that start with an empirical phenomenon and abstract from it to create general statements that can be verified by data [3]. Mid-range theories are dominant within empirical and scientific approaches to research. Gough usefully categorises such research as aiming to generate, explore, or test theories. Of particular importance in health literature are studies which include theories about cause and effect; such studies may test these theories in a ‘black box’ way or attempt to generate, explore, and test more clearly articulated causal-pathway frameworks, such as those presented in logic models [4]. For this discussion, the terms ‘causal pathway’, ‘causal maps’, and ‘logic model’ refer to qualitative models used to identify key concepts and the links between them [5]. Within the health sciences, it is widely understood that individual and population health are influenced by a wide array of interconnecting factors, so theoretical models can be complex and, at times, contested [6]. However, different disciplines approach such research in different ways and are not always well connected. Reviews of theory may aid our attempts to navigate a diverse literature and potentially lead to insights into how factors relate to one another [6-9]. Theory reviews could have one or more of the following aims: identifying and mapping a comprehensive range of relevant theories; assessing which theories have become influential and which have been, or have become over time, largely overlooked; and integrating complementary theories and facilitating the analysis and synthesis of theories into more generalised or abstract ‘meta-theories’. By focusing on theory, rather than diverse empirical studies, reviews can be useful devices to describe complex topics across different disciplines and inform policy debates. The purpose of this article is to consider the ways in which theoretical reviews might be conducted and in particular the role of systematic approaches within this. It illustrates the discussion by drawing on the approach of a recent theoretical review the authors undertook of income and health [10]. It discusses some of the methodological challenges and options that reviewers may face Page 2 of 11 when planning and conducting reviews that focus on theoretical literature. We think the discussion will be particularly relevant to reviewers considering the degree to which they might attempt to use and adapt methods commonly associated with systematic reviews, which tend to have been developed around reviews of empirical research and thus not specifically designed to assess descriptions of theories underpinning research. We will discuss the extent to which methods devel (...truncated)