Interaction Effects in the Theory of Planned Behavior: The Interplay of Self-Identity and Past Behavior


Correspondence concerning this article should be addressed to Joanne R. Smith, School of Psychology, University of Exeter, Exeter, United Kingdom. E-mail:


This research used a revised theory of planned behavior (TPB) model, which incorporated self-identity and past behavior—and the interaction between these constructs—in order to improve the model's predictive power in relation to consumer behavior (purchasing one's preferred beer). At Time 1, respondents (N = 108) completed measures of attitudes, perceived behavioral control, subjective norm, self-identity, past behavior, and intentions. Behavior was assessed 1 week later. All predictors were positively related to intentions. Self-identity and past behavior interacted to influence intentions: Self-identity had a stronger influence on intentions at low, rather than high, levels of past behavior. Intentions and past behavior were predictive of Time 2 behavior. These findings emphasize the need to consider identity issues in the TPB.