Theory of Planned Behavior

Imagine that your friend is trying to start exercising more regularly. According to the Theory of Planned Behavior (TPB), her decision to engage in this new routine is influenced by three key factors: attitude, subjective norms, and perceived behavioral control. 

Let’s first examine her attitude. Her new positive feelings toward exercise might stem from an article she read about how regular workouts will improve her physical health, boost her mood, and help her regulate hormonal fluctuations. Obviously, these all sound great, so she’s excited and highly motivated to start the new workout program. 

How about subjective norms—how will the environment affect her behavior? Your shared social circle has also likely played a significant role in her decision. Maybe a lot of your friends are fitness-focused—posting their achievements on Strava, going to yoga in the park, and joining run clubs. She might feel encouraged (or even slightly pressured) to join along, knowing that her friends will support her fitness journey and cheer her on as she pursues her athletic goals.

Lastly, let’s consider her perceived behavioral control. Your friend’s actual ability to start a new behavior (in this case, going to the gym) will also influence her decision. Luckily, she lives close to a gym, has a flexible work schedule, can easily afford a membership, and has plenty of friends who can offer up training advice. With all of this, she now feels confident that she can start incorporating regular exercise into her week!

The Theory of Planned Behavior would suggest that your friend’s positive attitude towards exercising, the social encouragement she receives from her environment, and her confidence in overcoming any logistical barriers all align to form her intention to start working out. This theory builds on the Theory of Reasoned Action (TRA) by adding the concept of perceived behavioral control, which addresses factors outside of the individual's control that might influence behavior.

The core component of the Theory of Planned Behavior (TPB)

Attitudes toward the Behavior 

This refers to the individual's positive or negative evaluations of performing a specific behavior. If a person believes that the behavior will lead to favorable outcomes, then they’re more likely to have a positive attitude towards it—contributing to their willingness. For example, if you think that cycling to the office will get you there faster than driving, then you might be more motivated to cycle. 

Subjective Norms

Subjective norms refer to the social pressure to perform or not perform a particular behavior. Our comportment is influenced by what we believe others expect of us, this can mean the perceived expectations of our friends, family, and society as a whole. For example, you may work in an office with a big cycle culture—with many coworkers using this as their main transport to get to work. The presence of social and cultural pressure may contribute to your inclination to follow suit.

Perceived Behavioral Control

Perceived behavioral control is a key component that distinguishes the Theory of Planned Behavior from the Theory of Reasoned Action. It refers to an individual’s perception of how easy or difficult it will be to perform a specific behavior, based on their past experiences, anticipated obstacles, and available resources.²

This concept encompasses both internal factors, like confidence in one's abilities, and external factors, such as the presence of barriers or facilitators. For example, if you’re deciding between cycling or driving to work you might be more inclined to cycle if you realize your car is out of gas or if there’s a major traffic jam, as these obstacles make driving seem more difficult.

Together, these components shape an individual's intention to perform a behavior, which is the antecedent to the actual implementation. The stronger the intention, the more likely the behavior will be performed, provided that the individual has adequate control over the behavior. Even if someone has a strong intention to perform a certain action, they must feel genuinely capable of overcoming any obstacles that might arise. For example, no matter how much your friend may want to take up running, if she trips and breaks her leg she will have to put off achieving this goal. 

Behavioral Intention: The motivational factors that influence a given behavior; an indication of an individual's readiness to perform the behavior.

Social Norms: These are the informal rules that guide behavior within society. Generally, they are a means of constraining behavior.

Self-Efficacy: The belief in one's ability to successfully execute a specific task or achieve a goal. It influences how individuals approach challenges, with higher self-efficacy leading to greater confidence and persistence, while lower self-efficacy can result in doubt and avoidance.

Behavioral Beliefs: Beliefs about the likely outcomes of the behavior and the evaluations of these outcomes.

Normative Beliefs: An individual’s perceptions about the expectations and behaviors of specific referent people or groups concerning a particular behavior.

Control Beliefs: Beliefs about the presence of factors that may facilitate or impede performance of the behavior and the perceived power of these factors.

Theory of Reasoned Action: TRA posits that when both the attitude toward the behavior and the subjective norms are favorable, the intention to perform the behavior is strong, which increases the likelihood of the behavior actually being carried out. However, TRA assumes that behavior is under volitional control, meaning that individuals can freely decide whether to engage in the behavior without significant external constraints.

Icek Ajzen, a social psychologist, developed the Theory of Planned Behavior in 1985. This theory was actually an extension of the Theory of Reasoned Action, which he had co-developed with psychologist Martin Fishbein in the mid-70s. 

The Theory of Reasoned Action (TRA) was focused on attitude and attitude change, and combined learning theories, expectancy-value theories, attribution theory, and consistency theories. The basic idea behind TRA is that attitudes and subjective norms are highly correlated with behavioral intention, and behavioral intention is correlated with actual behavior.^1,2 This means that individuals are more likely to engage in a particular behavior if they have a positive attitude toward it and perceive that important others expect them to do it.

But, Ajzen later recognized that this theory didn’t account for behaviors over which individuals have incomplete control, where external factors, situational constraints, or limitations in personal resources influence the ability to perform the behavior. To address this limitation, he introduced the concept of perceived behavioral control in the Theory of Planned Behavior. This addition aimed to capture a more nuanced understanding of behavior by incorporating elements of self-efficacy and control beliefs. 

Since its inception, the Theory of Planned Behavior has undergone various refinements and has been applied across diverse domains. Its versatility and robustness have made it one of the most influential models in behavioral science, offering valuable insights into the prediction and understanding of human behavior.

The application of the TPB has had profound implications for designing interventions and policies aimed at changing behavior. When we understand the factors that influence behavioral intentions, we can develop targeted strategies to promote desired behaviors. Let’s look at some of the main areas where the theory has been effectively applied:

Health Psychology

The Theory of Planned Behavior has been used to help us understand so much about how patients handle illness, why some people don't follow medical advice, and finding the most effective ways to control pain. 

It has helped design interventions to increase physical activity³, promote smoking cessation⁴, and enhance adherence to medical treatments.⁵ For example, in promoting physical activity, interventions based on the theory might focus on enhancing positive attitudes by highlighting the health benefits of exercise. This can also lean on the power of subjective norms by encouraging social support for physical activity: if everyone is talking about how good it feels to exercise, how much fun they’re having, or all the new friends they’ve made in their exercise classes, these may be powerful influences! 

Following the same example, we could also focus on increasing perceived behavioral control by providing information on how to overcome common barriers. Maybe someone feels like they simply don’t have enough time to exercise. Are they aware they could get to work faster by cycling instead of driving? Or that exercise doesn’t have to mean training like an olympian? Maybe they don’t currently own a bike. Could we let people know about certain bike-rental schemes across the city? Addressing the key barriers can be incredibly helpful in empowering people to take charge of their health.

TPB for the Environment 

The Theory of Planned Behavior has been instrumental in promoting environmentally friendly behaviors like recycling, energy conservation, and using sustainable transportation.⁶ Understanding the psychological determinants of these behaviors allows policymakers and practitioners to craft messages or design initiatives that resonate with the target audience in mind. For instance, campaigns to reduce energy consumption might focus on changing attitudes by emphasizing the environmental and financial benefits of energy-saving behaviors. They might ask people ‘do you know how much money you can save on gas by cycling to work?’ or ‘Do you know how many gallons of water you could save by choosing a plant-based meal?’, and then educating them on how these small changes could lead to large impacts.⁶ 

Additionally, educational and informative campaigns can influence subjective norms by showcasing the widespread social approval of such behaviors, like calling attention to the fact that over 1.5 billion people are vegetarian or that 30% of people in Germany regularly bike to work.⁸ Campaigns can also increase perceived behavioral control by providing easy-to-follow energy-saving tips, like suggesting that employees choose lunch items that don’t include meat or dairy and bike to work on days when it’s nice outside.

Promoting a Behavior as an Organization 

In organizational settings like offices, the theory has been applied to understand and influence behaviors like employee productivity, adherence to safety protocols, and participation in training programs. By identifying the attitudes, subjective norms, and perceived behavioral controls that influence these behaviors, organizations can develop targeted interventions to enhance employee engagement and performance.⁹ For instance—if we return to the biking example—to improve adherence to safety protocols, an organization might focus on changing attitudes by communicating the importance of safety (wearing a helmet while biking can mean the difference between a scratched noggin and permanent brain damage), leveraging subjective norms by fostering a safety culture (a sign could state that 80% of fellow employees wear their helmets when biking to work) and increasing perceived behavioral control by providing the necessary training and resources (teaching road safety and turn signals for bikers).

Despite its widespread application and empirical support, the Theory of Planned Behavior has faced several criticisms and controversies. One of the first main points of contention is that the theory assumes behavior is the result of a “rational” decision-making process. Critics argue that this overlooks the role of emotions, habits, and unconscious influences on behavior. 

For example, habitual behaviors or impulsive actions may not always align with the “rational deliberation” posited by the Theory of Planned Behavior. Just like how behavioral economics recognizes that we are human beings who are always making choices in the context of a much broader environment (social, cultural, emotional, physical), we must acknowledge that there are many forces that affect our behavior which may not be captured by a singular theory, and our internal emotions could definitely be one such force. 

Structural barriers such as socioeconomic status, access to resources, and policy frameworks can significantly impact behavior, and these factors may not be fully captured by the components of the theory. If we think back on our example of driving versus cycling to work, how might social class impact this decision? While cycling to work may be cheaper in the long run (by saving gas money over the course of several weeks or months), someone living with a lower income may not be able to afford the upfront costs associated with purchasing a bike. 

The measurement of perceived behavioral control has also been a point of controversy. Some researchers argue that this construct is often conflated with self-efficacy, leading to inconsistencies in its operationalization and measurement. “Self-efficacy” refers to an individual's belief in their ability to perform a specific task, while “perceived behavioral control” encompasses both the individual's belief in their ability and the perceived availability of resources and opportunities. This distinction is important, but not always clearly maintained in empirical research, leading to results and interpretations which can be misinterpreted or even purposely misconstrued.

Lastly, the predictive power of the Theory of Planned Behavior has been questioned, with some studies showing that the theory explains only a modest proportion of the variance in behavior. While the theory has been successful in predicting intentions, the translation of these intentions into actual behavior is not always straightforward. Various external factors and unmeasured variables can influence whether intentions lead to behavior, highlighting the need for a more comprehensive approach to understanding and predicting behavior. No theory is perfect, and there will always be gaps when trying to explain or understand something as complex as human behavior through just one perspective. 

In 2013, a group of researchers tried to predict the physical activity intention and behavior of middle and high school students in Hong Kong by applying the Theory of Planned Behaviour. These researchers were trying to address the growing concern of physical inactivity among adolescents, as regular physical activity is linked to various health benefits and chronic disease prevention. The study used the theory to understand and potentially improve the physical activity levels of students.

The study was made up of 486 students, aged 11 to 18, and collected data through self-administered questionnaires that measured demographic information, past physical activity, and variables such as attitude, subjective norms, and perceived behavioral control (the components related to the TPB). The study was conducted in two phases: the first phase involved the initial distribution of questionnaires, while the second phase, conducted eight weeks later, measured the physical activity behavior of the students.

The study found that approximately 75% of students did not meet the recommended physical activity standards, with males showing higher behavioral intentions and perceived behavior control compared to females. The Theory of Planned Behavior variables explained 53% of the variance in physical activity intentions, meaning that the differences in their intents to exercise could be explained but the theory. However, when predicting actual physical activity behavior, the theory accounted for only 26% of the variance, but this is still powerful. 

The findings confirmed that the Theory of Planned Behavior model is a useful framework for predicting physical activity intentions (at least among adolescents in Hong Kong). It suggests that public health interventions should focus on enhancing perceived control and leveraging past behaviors to promote physical activity and highlights the importance of addressing gender differences and ensuring that health promotion strategies are tailored to effectively target both boys and girls.¹⁰

The Intention Action Gap: The intention-action gap describes the discrepancy between our intentions, or what we plan to achieve, and our actual actions, or what we ultimately do. This occurs because we are naturally inclined toward immediate gratification, which can lead us to prioritize short-term rewards, regardless of our underlying attitudes, beliefs, and values.

Disgusting decision-making with Yoel Inbar: In this podcast episode of the Decision Corner, listen to Brooke as he speaks with Yoel Inbar – professor of psychology at the University of Toronto and expert in how the feeling of disgust influences human judgment and decision-making. Together they define what it really means to feel a sense of disgust and its evolutionary purpose as a means of preventing risk or harm (like stopping us from eating rotten food!). On the flip-side, we hear about the negative consequences of disgust and why it can lead to biased or flawed judgements. 

1. Ajzen, Icek. (1991). The Theory of Planned Behavior. Organizational Behavior and Human Decision Processes. 50. 179-211. 10.1016/0749-5978(91)90020-T. 
2. Madden, T. J., Ellen, P. S., & Ajzen, I. (1992). A Comparison of the Theory of Planned Behavior and the Theory of Reasoned Action. Personality and Social Psychology Bulletin, 18(1), 3-9. https://doi-org.gate3.library.lse.ac.uk/10.1177/0146167292181001 
3. Shafieinia, M., Hidarnia, A., Kazemnejad, A., & Rajabi, R. (2016). Effects of a Theory Based Intervention on Physical Activity Among Female Employees: A Quasi-Experimental Study. Asian journal of sports medicine, 7(2), e31534. https://doi-org.gate3.library.lse.ac.uk/10.5812/asjsm.31534 
4. Tapera, R., Mbongwe, B., Mhaka-Mutepfa, M., Lord, A., Phaladze, N. A., & Zetola, N. M. (2020). The theory of planned behavior as a behavior change model for tobacco control strategies among adolescents in Botswana. PloS one, 15(6), e0233462. https://doi-org.gate3.library.lse.ac.uk/10.1371/journal.pone.0233462 
5. M. Kopelowicz, A., Zarate, R., Wallace, C. J., Liberman, R. P., Lopez, S. R., & Mintz, J. (2015). Using the theory of planned behavior to improve treatment adherence in Mexican Americans with schizophrenia. Journal of consulting and clinical psychology, 83(5), 985–993. https://doi-org.gate3.library.lse.ac.uk/10.1037/a0039346 
6. Yuriev, A., Dahmen, M., Paillé, P., Boiral, O., & Guillaumie, L. (2020). Pro-environmental behaviors through the lens of the theory of planned behavior: A scoping review. Resources, Conservation and Recycling, 155, 104660. https://doi.org/10.1016/j.resconrec.2019.104660
7. Phoenix, Sam. (2024, March 29). Vegetarian statistics 2024: Surprising facts & data. Great Green Wall. https://www.greatgreenwall.org/supplements/vegetarian-statistics/
8. Marshall, John. (2021, September 18). Germans and their beloved bike paths. Deutsche Welle. https://www.dw.com/en/germans-and-their-beloved-bike-paths/a-59215483
9. Hemsworth, D., Muterera, J., Khorakian, A., & Garcia-Rivera, B. R. (2024). Exploring the Theory of Employee Planned Behavior: Job Satisfaction as a Key to Organizational Performance. Psychological Reports, 0(0). https://doi-org.gate3.library.lse.ac.uk/10.1177/00332941241252784
10. Mok, V., & Lee, A. (2013). A case study on application of the theory of planned behaviour: Predicting physical activity of adolescents in Hong Kong. Journal of Community Medicine & Health Education, 3(231). https://doi.org/10.4172/2161-0711.1000231