Extending the Theory of Planned Behavior: A Review and Avenues for Further Research

This paper describes and reviews the theory of planned behavior (TPB). The focus is on evidence supporting the further extension of the TPB in various ways. Empirical and theoretical evidence to support the addition of 6 variables to the TPB is reviewed: belief salience measures, past behaviodhabit, perceived behavioral control (PBC) vs. self-efficacy, moral norms, self-identity, and affective beliefs. In each case there appears to be growing empirical evidence to support their addition to the TPB and some under-standing of the processes by which they may be related to other TPB variables, inten-tions, and behavior. Two avenues for expansion of the TPB are presented. First, the possibility of incorporating the TPB into a dual-process model of attitude-behavior re-lationships is reviewed. Second, the expansion of the TPB to include consideration of the volitional processes determining how goal intentions may lead to goal achievement is discussed. The theory of planned behavior (TPB) is a widely applied expectancy-value model of attitude-behavior relationships which has met with some degree of success in predicting a variety of behaviors (Ajzen, 1988, 199 1, 1996a; Conner & Sparks, 1996; Godin & Kok, 1996). The TPB details the determinants of an in-dividual's decision to enact a particular behavior. Rather than review the evi