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 not to be 100% voluntary and under control, which resulted in the addition of perceived behavioral control. With this addition the theory was called the Theory of Planned Behavior.
Briefly, according to TPB, human action is guided by three kinds of considerations:
1. Behavioral Beliefs (beliefs about the likely consequences of the behavior)
2. Normative Beliefs (beliefs about the normative expectations of others)
3. Control Beliefs (beliefs about the presence of factors that may facilitate or impede performance of the behavior).
Ajzen's three considerations are crucial in circumstances / projects / programs when changing behavior of people.
As a general rule, the more favorable the attitude and subjective norm and the greater the perceived control, the stronger should be the person’s intention to perform the behavior in question.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 as many people think. A review of existing evidence suggests that the residual impact of past behavior is attenuated when measures of intention and behavior are compatible and 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 contributes to the prediction of later behavior only 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. Increasing knowledge alone does not help to change behavior very much. Campaigns that aim at attitudes, perceived norms and control in making the change or buying certain goods have better results.