Theory of Planned Behavior

An extension of the theory of reasoned action, the theory of planned behavior (TPB) is today one of the most popular models for explaining, predicting, and changing human social behavior. It has been applied to study a number of health behaviors, including exercise, smoking, drug use, and compliance with medical regimens. According to the TPB, human behavior is guided by three kinds of considerations:

• 1.
  Beliefs about the likely outcomes of the behavior and the evaluations of these outcomes (behavioral beliefs); in their aggregate, these beliefs produce a positive or negative attitude toward the behavior.
• 2.
  Beliefs about the normative expectations of important others and motivation to comply with these [Page 1033]expectations (normative beliefs) that result in perceived social pressure or a subjective norm.
• 3.
  Beliefs about the presence of various internal and external factors and the perceived power of these factors to facilitate or impede performance of the behavior (control beliefs). Collectively, control beliefs give rise to a sense of self-efficacy or perceived behavioral control.

Attitudes toward the behavior, subjective norms, and perceived behavioral control jointly lead to the formation of a behavioral intention. The relative weight or importance of each of these determinants of intention can vary from behavior to behavior and from population to population. However, as a general rule, the more favorable the attitude and subjective norm, and the greater the perceived control, the stronger the person's intention to perform the behavior in question. Finally, given a sufficient degree of actual control over the behavior, people are expected to carry out their intentions when the opportunity arises. Intention is thus assumed to be the immediate antecedent of behavior. However, because many behaviors pose difficulties of execution, the TPB stipulates that degree of control moderates the effect of intention on behavior: Intentions are expected to result in corresponding behavior to the extent that the individual has volitional control over performance of the behavior.

Beliefs serve a crucial function in the TPB; they represent the information people have about the behavior, and it is this information that ultimately guides their behavioral decisions. According to the TPB, human social behavior is reasoned or planned in the sense that people take into account the behavior's likely consequences, the normative expectations of important social referents, and factors that may facilitate or impede performance. Although the beliefs people hold may be unfounded or biased, their attitudes, subjective norms, and perceptions of behavioral control are thought to follow reasonably from their readily accessible beliefs, to produce a corresponding behavioral intention, and finally to result in behavior that is consistent with the overall tenor of the beliefs. However, this should not be taken to imply deliberate, effortful retrieval of information and construction of intention prior to every behavior. After a person has at least minimal experience with a behavior, his or her attitude, subjective norm, and perceived behavioral control are assumed to be available automatically and to spontaneously produce a behavioral intention.

In sum, the behavioral, normative, and control beliefs that are readily accessible in memory serve as the fundamental explanatory constructs in the TPB. Examination of accessible beliefs provides substantive information about the considerations that guide people's behavior and can thus also serve as the basis for interventions designed to change behavior.

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