A comparative case study illustrating the influence of a system perspective on the outcome evaluation of simple versus complex interventions

When evaluating the effectiveness of an intervention, the evaluation approach must match the intervention complexity, ensuring that the chosen evaluation is “fit for purpose.” For simple interventions, evaluating short-, mid-, and long-term outcomes is appropriate. However, for complex interventions, an additional outcome that must be considered is the essential system property that emerges as a result of the interaction of interdependent intervention components. By focusing on the emergent system property, evaluators are better able to assess the holistic effectiveness of a complex intervention. This article illustrates this principle through a comparative case study of a simple intervention and a complex intervention within a National Institute of Health (NIH) funded Clinical Translational Research center. The analysis illustrates that a more effective and appropriate evaluation results when a complex intervention, deemed to be operating and functioning as a system, is evaluated as a system than could have been achieved by treating each component as independent and evaluating the short-, mid-, or long-term outcomes of each component.