Creating space for theory when codesigning healthcare interventions

Designing healthcare interventions and the role of end users and stakeholders 
Improving healthcare by designing and testing theory-based interventions is widely recognised as gold-standard practice. Theory ‘presents a systematic way of understanding events or situations. It is a set of concepts, definitions, and propositions that explain or predict these events or situations by illustrating the relationships between variables.’¹ Using this definition, theory provides scaffolding for intervention design by clarifying how and why particular phenomena or behaviour occur, and the factors and mechanisms that might affect change.² By using theory to guide intervention design and its mechanisms of action, resulting interventions may have a stronger chance of success in creating their intended change.^{3, 4} The value of using and operationalising theory fully in healthcare interventions has long been recognised.⁴ Clearly articulating intervention techniques and their underlying theory facilitates their replication and evaluation.⁵ Improving interventions is also contingent upon understanding how key mechanisms contribute to outcomes and where to make changes. In contrast to the value ascribed to using theory in intervention design, the experiences and perspectives of individuals who may be likely to benefit from a given intervention have only recently been considered as an essential element for intervention design. With rapid acceleration in the use and value awarded to participatory methods in healthcare intervention design, those designing healthcare interventions must consider how to integrate knowledge from theory with that from individuals with lived experiences.^6-8