Phase IV implementation studies. The forgotten finale to the complex intervention methodology framework.

The complex intervention methodology framework defines the iterative process for developing and evaluating complex interventions in healthcare, but advice on implementation research was not included until the 2008 update. Our recent systematic review of implementation studies identified significant problems with reporting standards, including inconsistent terminology and crucial information that was missing or unclear. Introduction of reporting checklists has standardized the reporting of randomized controlled trials and other types of studies, and there is a need for similar guidance for reporting implementation studies. Key standards might include an explicit evidence base from a randomized controlled trial or guideline recommendation; recruitment to the clinical service, not the research; at least some outcomes at the population level using routinely collected data; and a description of the setting and the process of implementing the service. The complex intervention framework currently illustrates a cycle of development and evaluation, which includes implementation as a final step. We propose that the research underpinning implementation should be visualized as a second interrelated cycle. Just as the "phase III cycle" includes the iterative steps of development and piloting, a similar process may be needed to translate the intervention into a practical service that can be tested in a phase IV implementation study.