Untangling the Theory of Planned Behavior's auxiliary assumptions and theoretical assumptions: implications for predictive and intervention studies

It has been asserted that the Theory of Planned Behavior (TPB) is better at behavioral prediction than it is behavioral change. However, the performance of a theory depends not only on the theoretical propositions, but the auxiliary assumptions attached to the theory. It is because of such auxiliary assumptions, which are required to bridge the gap between nonobservational terms at the level of theory and the observational terms at the level of the empirical hypothesis, that we believe critiques of the TPB's utility are misguided. We argue that a failure to separate theoretical assumptions from auxiliary assumptions leads to this false assumption. We suggest the importance of distinguishing between the auxiliary assumptions required for prediction studies and the auxiliary assumptions required for intervention studies. We believe that in attaching sound auxiliary assumptions to intervention studies, the TPB is equally effective at facilitating behavior change as it is behavior prediction.