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Research Methods & Reporting

Process evaluation of complex interventions: Medical Research Council guidance

BMJ 2015; 350 doi: (Published 19 March 2015) Cite this as: BMJ 2015;350:h1258
  1. Graham F Moore, research fellow1,
  2. Suzanne Audrey, research fellow2,
  3. Mary Barker, associate professor of psychology3,
  4. Lyndal Bond, principal research officer4,
  5. Chris Bonell, professor of sociology and social policy5,
  6. Wendy Hardeman, senior research associate in behavioural science6,
  7. Laurence Moore, director7,
  8. Alicia O’Cathain, professor of health services research8,
  9. Tannaze Tinati, research fellow3,
  10. Daniel Wight, children, young people, families and health programme leader7,
  11. Janis Baird, associate professor of public health3
  1. 1DECIPHer UKCRC Public Health Research Centre of Excellence, School of Social Sciences, Cardiff University, Cardiff, UK
  2. 2DECIPHer UKCRC Public Health Research Centre of Excellence, School of Social and Community Medicine, University of Bristol, Bristol, UK
  3. 3MRC Lifecourse Epidemiology Unit, University of Southampton, Southampton, UK
  4. 4Centre of Excellence in Intervention and Prevention Science, Melbourne, VIC Australia
  5. 5Department of Childhood, Families and Health, Institute of Education, University of London, London, UK
  6. 6Primary Care Unit, Department of Public Health and Primary Care, University of Cambridge, Cambridge, UK
  7. 7MRC/CSO Social and Public Health Sciences Unit, University of Glasgow, Glasgow, UK
  8. 8School of Health and Related Research, University of Sheffield, Sheffield, UK
  1. Correspondence to: G F Moore MooreG{at}
  • Accepted 13 January 2015

Process evaluation is an essential part of designing and testing complex interventions. New MRC guidance provides a framework for conducting and reporting process evaluation studies

Attempts to tackle problems such as smoking and obesity increasingly use complex interventions. These are commonly defined as interventions that comprise multiple interacting components, although additional dimensions of complexity include the difficulty of their implementation and the number of organisational levels they target.1 Randomised controlled trials are regarded as the gold standard for establishing the effectiveness of interventions, when randomisation is feasible. However, effect sizes do not provide policy makers with information on how an intervention might be replicated in their specific context, or whether trial outcomes will be reproduced. Earlier MRC guidance for evaluating complex interventions focused on randomised trials, making no mention of process evaluation.2 Updated guidance recognised the value of process evaluation within trials, stating that it “can be used to assess fidelity and quality of implementation, clarify causal mechanisms and identify contextual factors associated with variation in outcomes.”3 However, it did not provide guidance for carrying out process evaluation.

Summary points

  • MRC guidance for developing and evaluating complex interventions recognised the importance of process evaluation within trials but did not provide guidance for its conduct

  • This article presents a framework for process evaluation, building on the three themes for process evaluation described in 2008 MRC guidance (implementation, mechanisms, and context)

  • It argues for a systematic approach to designing and conducting process evaluations, drawing on clear descriptions of intervention theory and identification of key process questions

  • While each process evaluation will be different, the guidance facilitates planning and conducting a process evaluation

Developing guidance for process evaluation

In 2010, a workshop funded by the MRC Population Health Science Research Network discussed the need for guidance on process evaluation.4 There was consensus that researchers, funders, and …

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