In this chapter, we have shown that theory addresses three broad essential questions in behavioral intervention research: why the intervention should work (development phases), how the intervention does work (evaluation phases), and how the intervention works in real settings (implementation phases). Without a theory base, one cannot understand why an intervention should work, how it works and for whom, and how it is best implemented in real-world settings. Theories can help inform the selection of delivery characteristics and also guide decision making during the implementation phase concerning what elements of the intervention are immutable and what elements can be modified. As most, if not all, behavioral interventions need to be adapted for delivery in practice and service settings, this is a critical function during the translation/implementation/dissemination phases. Thus, theories/conceptual frameworks are highly practical tools that behavioral interventionists must use throughout the pipeline for advancing an intervention.
The choice of a theory is up to the investigator—there is no one magical theory or best conceptual framework. Furthermore, as most interventions are complex and designed to mitigate multifaceted problems, behaviors, or unaddressed needs, more than one theory most likely will need to be employed. Despite the challenges of using theory, without a theory, an intervention will have limited success.