Developing and evaluating health interventions for the benefit of patients is notoriously difficult. This also applies to the discipline of nursing, owing to the complexity of nursing interventions. Following significant revision, the updated guidance of the Medical Research Council (MRC) adopts a pluralistic view to intervention development and evaluation, including a theory-based perspective. This perspective promotes the use of programme theory, aiming to understand how and under what circumstances interventions lead to change.

In this discussion paper, we reflect the recommended use of programme theory in the context of evaluation studies addressing complex nursing interventions. First, we review the literature by investigating the question, whether and how evaluation studies targeting complex interventions used theory and to what extent programme theories may contribute to enhance the theoretical foundations of intervention studies in nursing. Second, we illustrate the nature of theory-based evaluation and programme theories. Third, we argue how this may impact theory building in nursing in general. We finish by discussing which resources, skills and competencies are necessary to fulfill the demanding task of undertaking theory-based evaluations.

We caution against an oversimplified interpretation of the updated MRC guidance regarding the theory-based perspective, e.g. by using simple linear logic models, rather than articulating programme theories. Instead, we encourage researchers to embrace the corresponding methodology, i.e. theory-based evaluation.

With the prevailing perspective of knowledge production in crisis, we might be on the verge of a paradigm shift in health intervention research. Viewed through this lens, the updated MRC guidance could lead to a renewed understanding of what constitutes useful knowledge in nursing. This may facilitate knowledge production and, thereby, contribute to improve nursing practice for the benefit of the patient.