Background: The importance of theory is increasingly recognised in primary research and evidence synthesis. Indeed, an understanding of the theory underpinning interventions in disciplines such as health, social welfare and education can improve intervention design and implementation and may ultimately increase effectiveness. However, this critically depends on the appropriateness, quality and utility of a given theory to the research question at hand. A plethora of theories, frameworks or models in the literature have the potential to be of use, and how to identify, appraise and ultimately select the most relevant ones is not straightforward.

Objectives: We conducted a methodology review to identify existing systematic reviews of theories, models or frameworks as well as existing methodological guidance with a view to developing guidance on how to conduct systematic reviews of theories, frameworks or models. For this purpose, we specifically examined methods for searching, addressing the quality of, selecting and synthesising (where appropriate) and presenting or reporting theories.

Methods: We conducted systematic searches in MEDLINE and EMBASE, complemented by citation searches in Google Scholar and expert consultations. Studies meeting the pre-defined inclusion criteria were catalogued and relevant data extracted onto a table. Evidence synthesis was undertaken according to best-fit framework synthesis using the SALSA (Search, AppraisaL, Synthesis, Analysis) framework.

Results: Current systematic reviews of theories make suboptimal use of systematic searches, citation searches and expert consultation. While some reviews appraise aspects of the quality or utility of the theories identified, we did not identify a standardised tool that facilitates the systematic assessment of both the methodological quality and utility of a theory. Analysis of theories were thematic or framework based and results were presented narratively, in a table or graphically.

Conclusions: Current approaches to conduct methodology reviews are diverging. Based on the review we will developed a guidance on how to conduct systematic reviews of theories.