Current use was established and Cochrane guidance on selection of social theories for systematic reviews of complex interventions was developed

Objective: To identify examples of how social theories are used in systematic reviews of complex interventions to inform production of Cochrane guidance. Study Design and Setting: Secondary analysis of published/unpublished examples of theories of social phenomena for use in reviews of complex interventions identified through scoping searches, engagement with key authors and methodologists supplemented by snowball- ing and reference searching. Theories were classified (low-level, mid-range, grand). Results: Over 100 theories were identified with evidence of proliferation over the last 5 years. New low-level theories (tools, taxon- omies, etc) have been developed for classifying and reporting complex interventions. Numerous mid-range theories are used; one example demonstrated how control theory had changed the review’s findings. Review-specific logic models are increasingly used, but these can be challenging to develop. New low-level and mid-range psychological theories of behavior change are evolving. No reviews using grand the- ory (e.g., feminist theory) were identified. We produced a searchable Wiki, Mendeley Inventory, and Cochrane guidance. Conclusions: Use of low-level theory is common and evolving; incorporation of mid-range theory is still the exception rather than the norm. Methodological work is needed to evaluate the contribution of theory. Choice of theory reflects personal preference; application of theory is a skilled endeavor.