Testing theory in practice: The example of self-determination theory-based interventions

Leonardo da Vinci once said that, “He who loves practice without theory is like the sailor who boards ship without a rudder and compass and never knows where he may cast”. Similarly, advancing behavioral science requires a good understanding of how interventions are informed by theory, how they can better test theory, and which behavior change techniques should be selected as a function of theory (or theories) . However, simply claiming that an intervention is theory-based does not necessarily make it so. Critical evaluation of applied theory is needed for a more integrated understanding of behavior change interventions, their usefulness, and their effectiveness. The Theory Coding Scheme (TCS; Michie & Prestwich, 2010) was recently developed with the aim of providing a reliable research tool to describe and evaluate the theoretical basis of interventions. It includes a list of items assessing whether relevant constructs of a certain theory are targeted, how well they are measured, which behavior change techniques are used to impact those constructs, and whether study design allows for theory itself to be tested and refined. The TCS encourages a careful consideration of what constitutes a theory-based intervention (i.e. provides means for a more rigorous and systematic examination of the use of theory within intervention research), and how these interventions can be most usefully developed and evaluated serving as a structure to inform the design of theory-based interventions. A recent meta-analysis (Prestwich et al. , 2014) tested the application of the TCS, investigating i) the extent and type of theory use in health behavior change interventions to increase physical activity and healthy eating, and ii) the associations between theory use and intervention effectiveness. The authors found poor reporting on the application of theory in intervention design and evaluation. For example, few interventions targeted and measured changes in all theoretical constructs defined by the theory or linked all the behavior change techniques to those constructs. Since this meta-analysis tested the TCS framework with only two theories (Social Cognitive Theory [SCT] and the Transtheoretical Model), more research is needed to test the fidelity to theory in health behavior change interventions based on other frameworks and its differential impact on interventions effectiveness. One such framework is Self-Determination Theory (SDT; Deci & Ryan, 2000), which is increasingly being used in the area of behavioral nutrition and physical activity (Teixeira et al. , personal communication, May 22, 2014). In this paper we will focus on the development, implementation, and evaluation of theory-based interventions, using SDT as the example. This paper follows on the first two articles of this issue by Peters (2014) and Kok (2014), which highlight the importance of identifying and selecting theory-based constructs and appropriated methods to develop effective complex behavior change interventions.