Theory of Planned Behaviour

  • Developed by social psychologist Icek Ajzen in 1991
  • Extension of the Theory of Reasoned Action (Ajzen & Fishbein 1980)
  • The best Predictor of a behaviour is the intention of behaving that way.
  • Intentions in turn, are the product of only 3 factors: attitude, subjective norms and perceived behavioural control.

The 3 factors which build our intentions

Theory of Planned Behaviour (Fishbein, M. and Ajzen, I., 2010)

1. Attitude:

Attitude can be positive (increases likelihood of behaviour) or negative (reduces likelihood of behaviour). Attitude is based on two sub-factors:

    • affective attitude (emotion towards action)
    • instrumental attitude (regarding functional, objective benefits/risks of action).

2. Subjective norms:

Subjective norms are shaped by the perceived social pressure of others to behave in a certain way and by their willingness to follow the views of these individuals. Subjective Norms are based on two sub-factors:

    • injunctive norms (expected support of the social environment with regard to behaviour)
    • descriptive norms (witnessing social environment to also engage in behaviour)

3. Percieved behavioural control:

Feeling confident and able to handle the action (increases likelihood of behaviour) or feeling out of one’s comfort zone / unable to manage the tasks related to the behaviour (reduces likelihood of behaviour).

When do we take action?

To deduct whether a person will be taking action or not, we have to know what their intention is. The intention is based on the sum of the three factors above. Each factor has a manifestation which increases the probability to act and one which reduces it. By adding up the positive and negative values, the resulting intention towards the behaviour is positive or negative. Depending on the manifestation of the factors, the result, i.e. the intention, can be strong, medium or weakly negative / positive. The strength and direction (positive/negative) of the intention predict the likelihood of engaging in the behaviour.

Analysing an Example:

We want to know if Anna will start using a new jogging app regularly. To know if she will show the behaviour (using the jogging app), we want to find out what her intention looks like.

Therefore we take a look at the 3 factors which build her intention:

1. Attitude:

  • Affective attitude: Anna does not like the idea of using an app to become more active and healthy, 
    Negative: Decreases likelihood that she starts using the jogging app
  • Instrumental attitude: She knows that she could use some help to stay on track with her workout plan. Anna is aware that she needs to get fit in order to live a long and healthy life and the app could help her.
    Positive: increases likelihood that she starts jogging

2. Subjective norms:

  • Injunctive norms: Anna thinks that her husband would like her to get more fit and she thinks that he would support her using the jogging app.
    Positive: increases likelihood that she starts jogging
  • Descriptive norms: Every time she drives to work, Anna sees her neighbours jogging. Some of her friends talk about doing it as well.
    Positive: increases likelihood that she starts jogging

3. Perceived behavioural control:

  • Anna thinks that the app would be too complicated to use. She thinks that it would take her a long time to get accustomed to the app’s functions.
    Negative: reduces likelihood that she starts using the jogging app

Will Anna start using the jogging app?

Anna’s attitude is mixed and the subjective norms is rather positive, meaning that overall they are increasing the probability of Anna starting using the new jogging app. Only the perceived  behavioural control is clearly negative. To estimate the overall intention to use the app, however, we would need to scale the factors and sum the results. Developing such predictive models based on the TPB in various fields (such as sport apps) is a common application of this theory.

Criticism of TPB:

  • Since the theory is based on eliciting (already) existing beliefs about a behaviour, it cannot be applied to new behaviours, or new technologies, where the respondent has not yet formed beliefs toward.
  • Due to its high level of generality, the model does not provide recommendations on how to change (acceptance) behaviour
  • The three factors are conceptually distinct, but empirically found to be  correlated.

Advantages of TPB:

  • Applicability to a wide variety of behaviours 
  • Empirically tested theory
  • Incorporates the importance of social influence on behaviour

Field of Application:

Can be used to predict well established behaviours, such as exercising or dieting. Multiple studies confirm its applicability to innovation acceptance research. By applying the TPB model alone, however, only very limited insights can be derived for developing new technologies.

To learn more about the Diffusion Theory, visit the sources below:

Ajzen, I. and Fishbein, M. (1980), Understanding attitudes and predicting social behavior. Englewood Cliffs: Prentice-Hall.

Fishbein, M.and Ajzen, I.(2010), Predicting and changing behavior. The reasoned action approach. New York: Psychology Press.