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The Theory of Planned Behavior

By Elisabeth Brookes, published July 22, 2021


The theory of planned behavior (TPB) a cognitive theory by Azjen (1985) that proposes that an individual’s decision to engage in a specific behavior such as gambling or stopping gambling can be predicated by their intention to engage in that behavior (Fig. 1).

'Intentions are assumed to capture the motivational factors that influence a behavior; they are indications of how hard people are willing to try, of how much of an effort they are planning to exert, in order to perform the behavior. As a general rule, the stronger the intention to engage in a behavior, the more likely should be its performance' (Ajzen, 1991 p. 181).

According to TPB intentions are determined by three variables:

  1. Personal attitudes - This is our personal attitude towards a particular behavior.  It is the sum of all our knowledge, attitudes, prejudices …. positive and negative that we think of when we consider the behavior.  For example, our individual attitude to smoking might include tobacco is relaxing and makes me feel good but it makes me cough in the morning, costs a lot of money and smells bad.
  2. Subjective norms - This considers how we view the ideas of other people about the specific behavior e.g. smoking.  This could be the attitude of family and friends and colleagues to smoking. It is not what other people think but our perception of others’ attitudes.
  3. Perceived behavioral control - This is the extent to which we believe we can control our behavior. This depends on our perception of internal factors such as our own ability and determination and external factors such as the resources and support available to us. The theory argues that our perception of behavioral control has two effects: It affects our intentions to behave in a certain way i.e. the more control we think we have over our behavior, the stronger our intention to perform the behavior. It also affects our behavior directly, if we perceive that we have a high level of control we will try harder and longer to succeed. The present view of perceived behavioral control, however, is most compatible with Bandura*s (1977, 1982) concept of perceived self efficacy which ìs concerned with judgments of how well one can execute courses of action required to deal with prospective situationsî (Bandura, 1982, p. 122).

According to the model attitudes, subjective norms and perceived behavioral control
					predict the intention, which in turn predicts the behavior.

The theory of planned behavior is an extension of the theory of reasoned action (Ajzen & Fishbein, 1980; Fishbein & Ajzen, 1975)

According to the theory of planned behavior, perceived behavioral control, together with behavioral intention, can be used directly to predict behavioral achievement.


Health Applications

TPB has practical applications; it has been used in health education campaigns. Anti-drug campaigns often give data about the percentage of people engaging in risky behavior such as smoking or drug use to change the subjective norm.

For example, teenagers who smoke are usually are part of a peer group who smoke, therefore they might think smoking is the norm however most teenagers don’t smoke, so exposure to statistics showing them the true extent of smoking should change their subjective norm.

Applying the Theory of planned behavior to smoking

Applying the Theory of Planned Behavior to Smoking

TPB is the model most used in health psychology. It has been useful in predicting  intentions relating to smoking and drinking as supported by Hagger et al. (2011).

He found that the three of the components of the model (personal attitudes, subjective norms and perceived behavioral control) correlated with alcohol addicts’ intentions to limit or stop their drinking. 

He also found that those intentions were reflected in their behavior and could predict the approximate number of units consumed after 1 and 3 months. However it did not predict binge drinking.

Penny (1996) found that smokers were less likely to believe they would quit smoking and therefore were less likely to try, the more times they have failed to quit previously. This shows the importance of perceived behavioral control in shaping our intentions as predicted by TPB.

However, Webb et al. (2006) carried out a meta-analysis of 47 studies and found that although there is a link between intention and actual behavior, that link is small.

This suggests that there is a significant gap between intentions and behavior.


Critical Evaluation

There are methodological problems associated with research on this theory.

All the components of the model are assessed using questionnaires or interviews so the answers are influenced by social desirability. Furthermore, these interviews or questionnaires are done when the participants are not under the influence of drugs/ alcohol but when they are in the situations which trigger their addiction behavior (pub, party ….) their intentions might soon be forgotten and the behavior resumed.

A strength of TPB is that it takes into account the influence of peers (subjective norms) which is significant in both the beginning of the behavior and its maintenance (SLT and operant conditioning).

The theory of planned behavior assumes that all behaviors are conscious, reasoned and planned however it does not consider the role of emotions such as sadness, frustration … which can play an important role in influencing behavior.

About the Author

Elisabeth Brookes is an A-level psychology teacher, and author of her own website http://www.psychbug.co.uk/

How to reference this article:

Brookes, E. (2021, Sept 20). The theory of planned behavior. Simply Psychology. https://www.simplypsychology.org/theory-of-planned-behavior.html

APA Style References

Ajzen, I. (1985). From intentions to actions: A theory of planned behavior. In J. Kuhi & J. Beckmann (Eds.), Action-control: From cognition to behavior (pp. 11ó39). Heidelberg: Springer.

Ajzen, I. (1991). The theory of planned behavior. Organizational behavior and human decision processes, 50(2), 179-211.

Ajzen, 1., & Fishbein, M. (1969). The prediction of behavioral intentions in a choice situation. Journal of Experimental Social Psychology, 5, 400-416.

Ajzen, I., & Fishbein, M. (1970). The prediction of behavior from attitudinal and

normative variables. Journal of Experimental Social Psychology, 6, 466-487.

Ajzen, I., & Fishbein, M. (1977). Attitudeóbehavior relations: A theoretical analysis and review of empirical research. Psychological Bulletin, 84, 888-918.

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

Fishbein, M., & Ajzen, 1. (1975). Belief, attitude, intention, and behavior: An introduction to theory and research. Reading, MA: Addison - Wesley

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