- Rafael Perera, senior research fellow in statistics1,
- Carl Heneghan, deputy director1,
- Patricia Yudkin, reader in medical statistics2
- 1Centre for Evidence Based Medicine, Department of Primary Health Care, University of Oxford, Oxford OX3 7LF
- 2Department of Primary Health Care, University of Oxford
- Correspondence to:
- Accepted 15 November 2006
Complex interventions consist of several separate components combined to produce a desired outcome.1 Evaluation of such interventions in randomised trials will generally lead to complex comparisons between trial groups.2 Moreover, text descriptions in journal articles may obscure aspects of the interventions in the trial and hinder comparison between them. To counter these problems we have produced a single image that presents the components of all interventions in the trial and compares different treatment arms. The aim is to clarify the structure of the contrasted interventions and thus aid interpretation of the trial results.
The need for clear comparisons
We studied 169 randomised trials of non-drug interventions in primary care published between 1999 and 2003. We searched Medline, PSIQInfo, Bioabstracts, and Embase using the free text search terms “randomised controlled trials” and “primary care” and their synonyms, and excluding the term “placebo” appearing in the title or abstract; we also hand searched reference lists of retrieved papers. In many of these papers the interventions were incompletely described. We identified three principal problems: identifying the different components of the intervention, establishing the time at which components were delivered, and defining the differences between intervention arms.
To clarify these aspects we suggest that it would be helpful to depict the experimental and control interventions graphically. The proposed graph is similar to a flowchart, with each treatment arm represented in a specific column, …