Abstract
OBJECTIVE: Process evaluations (PEs) alongside randomised controlled trials of complex interventions are valuable because they address questions of for whom, how and why interventions had an impact. We synthesised the methods used in PEs of primary care interventions, and their main findings on implementation barriers and facilitators. DESIGN: Systematic review using the UK Medical Research Council guidance for PE as a guide. DATA SOURCES: Academic databases (MEDLINE, SCOPUS, PsycINFO, Cumulative Index to Nursing and Allied Health Literature, EMBASE and Global Health) were searched from 1998 until June 2018. ELIGIBILITY CRITERIA: We included PE alongside randomised controlled trials of primary care interventions which aimed to improve outcomes for patients with non-communicable diseases. DATA EXTRACTION AND SYNTHESIS: Two independent reviewers screened and conducted the data extraction and synthesis, with a third reviewer checking a sample for quality assurance. RESULTS: 69 studies were included. There was an overall lack of consistency in how PEs were conducted and reported. The main weakness is that only 30 studies were underpinned by a clear intervention theory often facilitated by the use of existing theoretical frameworks. The main strengths were robust sampling strategies, and the triangulation of qualitative and quantitative data to understand an intervention's mechanisms. Findings were synthesised into three key themes: (1) a fundamental mismatch between what the intervention was designed to achieve and local needs; (2) the required roles and responsibilities of key actors were often not clearly understood; and (3) the health system context-factors such as governance, financing structures and workforce-if unanticipated could adversely impact implementation. CONCLUSION: Greater consistency is needed in the reporting and the methods of PEs, in particular greater use of theoretical frameworks to inform intervention theory. More emphasis on formative research in designing interventions is needed to align the intervention with the needs of local stakeholders, and to minimise unanticipated consequences due to context-specific barriers. PROSPERO REGISTRATION NUMBER: CRD42016035572.