Theory of Planned Behavior

Theory of planned behavior is one of the most successful theories in social psychology; the theory aims to explain people's behavior in various domains—among them consumer behavior—by four psychological variables: intentions, attitudes, subjective norms, and perceived behavioral control.

The theory was introduced in an article by Icek Ajzen in 1991 and builds on the social psychological tradition of attitude research. It is an extended version of the preceding theory of reasoned action, developed by Ajzen and Martin Fishbein in the 1970s. Whereas the theory of reasoned action proved to be insufficient in many situations, the theory of planned behavior received strong empirical support since its publication and is still relevant for the explanation of consumer behavior. Although the theory was developed in the cultural context of the United States in the 1980s, extensive cross-cultural research confirmed that the basic structure of the theory is stable over time and cultures (e.g., Kalafatis, Pollard, East, and Tsogas 1999). However, the relative importance of the different aspects the theory covers changes between cultures and even situations.

The theory is general in nature and has been successfully applied to a wide array of different domains, including health behavior, ecological behavior, consumer behavior, leisure activities, and deviant behavior. It was developed to explain all kinds of actions that are performed deliberately, which means that performance of a behavior is preceded by a period of active weighing up of costs and benefits of an action and its alternative(s). Within the domain of consumer behavior, the theory applies to all kinds of purchase or consumer decisions that include active consideration of different types of costs and benefits, which includes more than monetary costs.

The theory of planned behavior has two basic assumptions: The first is that if people are given enough resources, in terms of cognitive capacity and time, they make a rational choice. It stands, therefore, in the tradition of rational choice theories, which assume that people integrate all available information about possible wins and losses of a behavioral alternative and choose the best possible alternative within this evaluation framework. However, rational choice does not imply that a decision for the objectively best alternative is made, because people might not have access to important pieces of information or may evaluate wins and losses or their probabilities incorrectly.

The second basic assumption of the theory of planned behavior (see Figure 1) is that the driving force behind an action in the domain of deliberate behavior is an intention. Having formed an intention signifies having broken the threshold between still weighing up benefits and costs and starting to plan how to perform the action. The intention, therefore, mentally represents the decision for just one alternative and the will to perform that behavior. The intention is automatically formed in a rational choice process considering three different aspects: attitudes, subjective norms, and perceived behavioral control.

An attitude toward an action is a general measure of how favorable a person considers the general outcome of this action. The attitude variable in the theory of planned behavior, therefore, subsumes the influence of evaluated information a person holds about an action and its alternatives. This measure of favorability is formed in a process of adding up all relevant positive and negative outcomes the person mentally connects to the action. These different single components are called behavioral beliefs. An attitude is, therefore, the sum of all accessible beliefs about the behavior in question. A belief consists of the assumption that a positive or negative aspect is related to an action multiplied by the probability that this outcome occurs. A moderately negative belief could thus be the result of an extremely negative outcome multiplied by a low probability or a moderate negative outcome multiplied by a high probability. Not all beliefs a person has about an action are accessible in every situation; usually just a subset of beliefs is activated, depending on the situation. This means that an attitude toward an action can vary even if the beliefs do not change.

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