Summary:
The Theory of Planned Behavior (TPB), developed by Icek Ajzen in 1985, aims to explain the processes by which people consciously decide to engage in a specific action. It expands on the earlier Theory of Reasoned Action, which focused on the role of attitudes and subjective norms in predicting behavior, by incorporating perceived behavioural control as an additional factor. TPB suggests that human behavior is primarily driven by behavioural intentions, which are determined by three core factors: attitudes, subjective norms, and perceived behavioural control. These factors combine to influence whether and how an individual will engage in a specific behavior.
- Attitudes: This refers to the individual’s evaluation of the behavior in question—whether they view it positively or negatively. If a person believes that the behavior will lead to favorable outcomes (i.e., they have a positive attitude toward it), they are more likely to engage in it. For instance, if someone believes that exercising regularly will improve their health, they are more likely to engage in physical activity.
- Subjective Norms: This involves the perceived social pressure to perform or not perform a behavior, based on the expectations of significant others such as family, friends, colleagues, or society at large. It reflects the individual’s motivation to comply with these perceived expectations. For example, if a person perceives that their peers believe it is important to recycle, they may be more likely to engage in recycling behaviors, even if they don't personally find it as important.
- Perceived Behavioural Control (PBC): This factor refers to the individual’s perception of how easy or difficult it is to perform the behavior, based on both internal factors (like skills or knowledge) and external factors (such as resources or opportunities). If an individual believes they have control over a behavior and can successfully perform it, they are more likely to intend to do so. For example, if someone perceives that they have access to a recycling bin and the time to recycle, they will be more likely to engage in recycling.
These three factors (attitudes, subjective norms, and perceived behavioral control) together determine an individual’s behavioural intention, which is the direct precursor to engaging in the behavior. Importantly, perceived behavioural control can also directly influence behavior, especially when actual control over the behavior is low. For example, if a person intends to exercise but perceives that they lack the time or resources (like a gym membership), they may not follow through on that intention, even if they have positive attitudes toward exercise and perceive social pressure to be active.
TPB emphasizes that human behavior is often the result of a deliberate, planned decision-making process. This makes it especially relevant in predicting consciously chosen behaviours—those that involve careful thought or planning, rather than spontaneous or automatic actions. The theory is particularly useful for understanding behaviors in contexts where individuals have some degree of control and awareness over their actions, such as health-related behaviors, environmental actions like recycling, and participation in civic activities such as voting.
While TPB can effectively predict behaviour, the theory also recognises that intentions do not always lead directly to action, as perceived behavioural control can act as a barrier. For instance, a person may have the intention to eat healthily and exercise regularly but may fail to do so due to external constraints like lack of time, financial limitations, or access to healthy food options.
An Application:
One key application of TPB is in health promotion campaigns. Public health interventions often aim to change behaviors related to smoking, alcohol consumption, physical activity, or nutrition. By focusing on improving attitudes (e.g., making people more aware of the benefits of quitting smoking), altering subjective norms (e.g., encouraging social acceptance of healthy eating), and increasing perceived behavioral control (e.g., making healthy food more accessible or providing support for quitting smoking), health campaigns can improve behavioral intentions and outcomes.
For example, a recycling campaign could use TPB to target individuals’ attitudes toward recycling (showing them its environmental benefits), increase perceived social pressure (reminding people that their peers or community values recycling), and improve perceived control (making recycling bins easily accessible and educating people on how to recycle properly). These strategies together would increase individuals' intention to recycle, and ultimately their actual behaviour.
In the voting behaviour context, TPB can be applied to predict who will vote in an election. People who have positive attitudes toward voting (believing it is important for democracy), perceive a social norm to vote (feeling that family or friends expect them to vote), and believe they have control over the voting process (having access to polling stations, time to vote) are more likely to express the intention to vote, and subsequently follow through with it. Campaigns to increase voter turnout can target these three factors, encouraging greater participation in democratic processes.
The TPB is less useful for predicting spontaneous behaviours like habits or 'gut instinct' - can you think of some reasons why?
Key References
Ajzen, I. (1985). From intentions to actions: A theory of planned behavior. In J. Kuhl & J. Beckmann (Eds.), Action control: From cognition to behavior. Berlin, Heidelber, New York: Springer-Verlag. (pp. 11-39).
This seminal chapter by Icek Ajzen presents the Theory of Planned Behaviour and details the components of attitudes, subjective norms, and perceived behavioural control, explaining how they combine to form behavioural intentions and predict behaviour.
Ajzen, I., & Fishbein, M. (1980). Understanding attitudes and predicting social behavior. Prentice-Hall.
This book outlines the Theory of Reasoned Action, which laid the foundation for the Theory of Planned Behaviour, and discusses how attitudes and norms influence human behaviour.
Armitage, C. J., & Conner, M. (2001). Efficacy of the Theory of Planned Behaviour: A meta-analytic review. British Journal of Social Psychology, 40(4), 471-499.
This meta-analysis provides a comprehensive review of studies applying the Theory of Planned Behaviour across various domains and demonstrates its effectiveness in predicting behaviours in health, social, and environmental contexts.
