Complex interventions are widely used in the health service, in public health practice, and in areas of social policy that have important health consequences, such as education, transport, and housing. They present various problems for evaluators, in addition to the practical and methodological difficulties that any successful evaluation must overcome. In 2000, the Medical Research Council (MRC) published a framework1 to help researchers and research funders to recognise and adopt appropriate methods. The framework has been highly influential, and the accompanying BMJ paper is widely cited.2 However, much valuable experience has since accumulated of both conventional and more innovative methods. This has now been incorporated in comprehensively revised and updated guidance recently released by the MRC (www.mrc.ac.uk/complexinterventionsguidance). In this article we summarise the issues that prompted the revision and the key messages of the new guidance.
- The Medical Research Council guidance for the evaluation of complex interventions has been revised and updated
- The process of developing and evaluating a complex intervention has several phases, although they may not follow a linear sequence
- Experimental designs are preferred to observational designs in most circumstances, but are not always practicable
- Understanding processes is important but does not replace evaluation of outcomes
- Complex interventions may work best if tailored to local circumstances rather than being completely standardised
- Reports of studies should include a detailed description of the intervention to enable replication, evidence synthesis, and wider implementation