Realistic evaluation of an emergency department-based mental health nurse practitioner outpatient service in Australia.

Evaluation of new models of care requires consideration of the complexity inherent within health care programs and their sensitivity to local contextual factors as well as broader community, social and political influences. Evaluation frameworks that are flexible and responsive while maintaining research rigor are therefore required. Realistic evaluation was adopted as the methodology for the implementation and evaluation of an emergency department-based mental health nurse practitioner outpatient service in Sydney, Australia. The aim of realistic evaluation is to generate, test and refine theories of how programs work within a given context. This paper represents the final methodological step from the completed evaluation. A summary of quantitative and qualitative findings from the mixed-methods evaluation is presented, which is transformed into a set of overarching statements or "middle range theories". Middle range theory statements seek to explain the success of a program and provide transferable lessons for practitioners wishing to implement similar programs elsewhere. For example, the research team consider that early consultation with key local stakeholders and emergency department ownership of the project was pivotal to the implementation process.