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The Theory of Planned Behavior (TPB) of Icek Ajzen (1988, 1991) helps to understand how we can change the behavior of people. The TPB is a theory which predicts deliberate behavior, because behavior can be planned.

TPB is the successor of the similar Theory of Reasoned Action of Ajzen and Fishbein (1975, 1980). The succession was the result of the discovery that behavior appeared to be not 100% voluntary and under control. This resulted in the addition of perceived behavioral control. With this addition the theory was called the Theory of Planned Behavior.

The three considerations of the Theory of Planned Behavior

In short, according to TPB, human action is guided by three kinds of considerations:

1. Behavioral Beliefs. These are beliefs about the likely consequences of the behavior.
2. Normative Beliefs. These are beliefs about the normative expectations of others.
3. Control Beliefs. These are beliefs about the presence of factors that may facilitate, or may impede, the performance of the behavior.

Ajzen Theory of Planned Behavior TPBThe three considerations of Ajzen are crucial in circumstances / projects / programs when the behavior of people needs to be changed.

In their respective aggregates, behavioral beliefs produce a favorable or unfavorable attitude toward the behavior, normative beliefs result in perceived social pressure or subjective norm, and control beliefs give rise to perceived behavioral control. In combination, the attitude toward the behavior, subjective norm, and perception of behavioral control, lead to the formation of a behavioral intention. As a general rule, if the attitude and subjective norm are more favorable, the perceived control will be greater, and the person’s intention to perform the behavior in question should be stronger.

Residual Effects of Past on Later Behavior

Recently (2002), Ajzen investigated residual effects of past on later behavior. He came to the conclusion that this factor indeed exists, but cannot be described to habituation, such as many people are thinking. A review of existing evidence suggests that the residual impact of past behavior is attenuated, when measures of intention and behavior are compatible. And the impact vanishes when intentions are strong and well formed, expectations are realistic, and specific plans for intention implementation have been developed.

A research project in the travel industry resulted in the conclusion that past travel choice only contributes to the prediction of later behavior if circumstances remain relatively stable.

Example: The Theory of Planned Behavior of Ajzen can help to explain why advertising campaigns merely providing information do not work. To only increase the knowledge does not help to change the behavior very much. Campaigns that aim at attitudes, perceived norms, and control in making the change or buying certain goods, have better results.

Similarly in management, programs that focus only on explanation of the importance of something (knowledge transfer) will likely not succeed. Rather one should convince people to change their intention to change, by giving a lot of attention to attitudes, subjective norms and perceived behavior control.

Book: Icek Ajzen, Martin Fishbein – Understanding Attitudes and Predicting Social Behavior