The Theory of Planned Behaviour (TPB) of Icek Ajzen (1988, 1991) helps to understand how we can change the behaviour of people. The TPB is a theory which predicts deliberate behaviour, because behaviour 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 behaviour appeared to be not 100% voluntary and under control. This resulted in the addition of perceived behavioural control. With this addition the theory was called the Theory of Planned Behaviour.
According to TPB, human action is guided by three kinds of considerations:
Behavioural Beliefs. These are beliefs about the likely consequences of the behaviour.
Normative Beliefs. These are beliefs about the normative expectations of others.
Control Beliefs. These are beliefs about the presence of factors that may facilitate, or may impede, the performance of the behaviour.
The three considerations of Ajzen are crucial in circumstances / projects / programs when the behaviour of people needs to be changed.
In their respective aggregates, behavioural beliefs produce a favourable or unfavourable attitude toward the behaviour, normative beliefs result in perceived social pressure or subjective norm, and control beliefs give rise to perceived behavioural control. In combination, the attitude toward the behaviour, subjective norm, and perception of behavioural control lead to the formation of a behavioural intention. As a general rule, if the attitude and subjective norm are more favourable, the perceived control will be greater, and the person’s intention to perform the behaviour in question should be stronger.
Recently (2002), Ajzen investigated residual effects of past on later behaviour. 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 behaviour is attenuated, when measures of intention and behaviour 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 behaviour if circumstances remain relatively stable.
Example: The Theory of Planned Behaviour 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 behaviour 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 behaviour control.