Randomised controlled trials are widely accepted as the most reliable method of determining effectiveness, but most trials have evaluated the effects of a single intervention such as a drug. Recognition is increasing that other, non-pharmacological interventions should also be rigorously evaluated.1–3 This paper examines the design and execution of research required to address the additional problems resulting from evaluation of complex interventions—that is, those “made up of various interconnecting parts.”4 The issues dealt with are discussed in a longer Medical Research Council paper (www.mrc.ac.uk/complex_packages.html). We focus on randomised trials but believe that this approach could be adapted to other designs when they are more appropriate.
- Complex interventions are those that include several components
- The evaluation of complex interventions is difficult because of problems of developing, identifying, documenting, and reproducing the intervention
- A phased approach to the development and evaluation of complex interventions is proposed to help researchers define clearly where they are in the research process
- Evaluation of complex interventions requires use of qualitative and quantitative evidence