The theory of planned behavior is a model that predicts human behavior based on three factors: personal attitudes, subjective norms, and perceived behavioral control.
For several decades, psychologists have attempted to develop models that could predict human behavior. However, it has proven to be quite difficult.
As Ajzen (1991) points out,
“…general dispositions tend to be poor predictors of behavior in specific situations…. In a similar fashion, the low empirical relations between general personality traits and behavior in specific situations…have been disappointing”
(Ajzen, 1991, p.180)
Therefore, Ajzen proposed the theory of planned behavior, which identifies several factors that determine the likelihood that an individual will initiate an action.
Theory of Planned Behavior Definition
The theory of planned behavior believes that behaviors can be predicted by looking at three key factors.
The three key factors that are said to predict peoples behaviors are:
- Personal attitudes – If we want to predict a person’s future behaviors, we need to look at their personal attitudes. For example, if a person has a positive attitude toward exercising, then they’re more likely to go to the gym.
- Subjective norms – If we want to predict a person’s future behavior, we need to look at the social and cultural norms they adhere to. For example, if someone’s culture glorifies and celebrates soccer, then the person may be more likely to play soccer.
- Perceived behavioral control – If we want to predict a person’s future behavior, we need to look at how much they believe they can control their own behavior and whether they can achieve change through effort (see also: locus of control theory).
Ajzen’s (1991) scholarly definition is provided below:
“Attitudes toward the behavior, subjective norms with respect to the behavior, and perceived control over the behavior are usually found to predict behavioral intentions with a high degree of accuracy”
(Ajzen, 1991, p.206)
Theory of Planned Behavior Examples
- Attitude to exercise predicting likelihood of exercising (personal attitude): Alice likes to exercise, it makes her feel tired, but also refreshed.
- Friends not going to the gym so you’re less likely to (subjective norm): None of Ben’s friends go to the gym or do any form of exercise because they are always playing video games.
- Belief that you can lose weight so you are more likely to try (perceived behavioral control): Sam knows that he can lose weight if he wants to by controlling his diet and riding a bike everyday.
- Attitude to modern medicine predicting treatment choice (personal attitude): Joon thinks that holistic health is an old idea and that modern medicine is much more beneficial in the long run.
- Attitude to yoga being linked to social norms in your country (subjective norm): Kumar does yoga or meditation every day because it is common practice in his home country.
- Belief in ability to quit smoking linked to previous experience of trying (perceived behavioral control): Mrs. Rodriguez stopped trying to quit smoking because she tried before and always failed.
- Disliking sports predicting you won’t participate (personal attitude): Janelle doesn’t care much for sports, even though she is tall and her dad wants her to play volleyball or basketball.
- A society’s gender norms predicting a person’s likelihood to go into a profession (subjective norm): Stan thinks that being a nurse seems like an odd profession for a male, so he hasn’t signed up for any nursing courses.
- A person choosing a career based on which subjects he thinks he can succeed in (perceived behavioral control): Minato is majoring in engineering because he is very good at mathematics and physics
- A person choosing a career based on their likes and dislikes (personal attitude): Maria became a graphic designer because she likes the combination of art and technology.
Theory of Planned Behavior Strengths and Weaknesses
| Strengths | Weaknesses |
|---|---|
| The theory has a wider diversity of contributing factors than other theories of motivation, such as the locus of control theory, which only focuses on one of the three factors examined in the theory of planned behavior. | The theory may not necessarily accurately predict behavior all of the time. This is particularly true if unexpected events or factors occur during a scenario that cannot fit into the three categories in the theory. |
| The theory has a substantive number of empirical studies backing it, reflecting its usability, applicability, and ability to stand up to rigorous testing. | The theory fails to look at subconscious factors that may affect decision making. It tends instead to focus on conscious decision-making processes. This focus on the conscious mind may not fully capture the complexity of human behavior. |
| The theory’s use of subjective norms helps it to take into account cultural factors, making it applicable across various social and cultural contexts. | The theory doesn’t spell out a spectrum of motivations, unlike other motivation theories such as the self-determination theory. |
Case Studies
1. The Wheeling Walks Campaign
A sedentary lifestyle has been linked to the development of numerous health problems. Fortunately, even exercise as simple as walking can help prevent some of those issues from becoming a serious health crisis.
The Wheeling Walks campaign took place in Wheeling West Virginia and was designed to increase walking among residents 50-65 years old.
The campaign:
“used theory of planned behavior . . . constructs to change behavior by promoting 30 minutes of daily walking through paid media, public relations, and public health activities”
(Reger et al., 2002, p. 285)
For example, pilot research revealed that sedentary adults believed they did not have time to exercise. So, the campaign included specific statements targeting that belief by suggesting residents start with just 10-minutes of walking each day, then 20, etc.
“The results indicate that 30% of Wheeling’s sedentary residents increased their walking to the recommended level compared to a 16% increase in a control community. Wheeling thus experienced a 14% net increase.”
Some of this program’s training materials can be found here.
2. Environmental Psychology
The theory of planned behavior has been applied in the area of environmental psychology to increase behaviors that improve environmental sustainability.
Engaging in environmentally friendly acts as a positive normative belief. However, there is also a lack of perceived behavioral control in the sense that some individuals believe that such actions will not have an impact on the environment or climate change.
Masud et al. (2016) assessed the theory of planned behavior model by examining the relation between personal attitudes toward climate change, perceived behavioral control, and opinions of people close to the research participants (i.e., subjective norm).
The study performed a confirmatory factor analysis (CFA) on questionnaires that assessed each dimension of theory of planned behavior which were distributed to residents in Selangor, Malaysia.
In the words of the authors:
“The key findings of this study indicate that attitudes, subjective norm and perceived behavioural control have positive influence on behavioural intention to adapt/mitigate climate change” (p. 613).
Although not without limitations, the results supported theory of planned behavior as a viable framework for understanding behavior in the context of environmental actions towards climate change.
3. Constructing A Valid Measure
One of the biggest challenges in psychology has to do with measurement. For instance, how do you measure a personality trait, or a person’s attitude towards a controversial issue?
In the hard sciences like physics and chemistry, there are numerous technologies that can measure constructs to the millionth decimal.
But in psychology, that’s just not possible. Instead, researchers often must rely on paper-and-pencil measurements, such as questionnaires and surveys.
Fortunately, Ajzen provides a tutorial on how to construct theory of planned behavior measures.
For example, if trying to measure subjective norms, research participants are asked questions about what other people think and do.
They are instructed to read a statement and then indicate the extent to which they agree or disagree by placing a mark next to the appropriate number.
Subjective Norm Questions
Most people who are important to me approve of my exercising for at least 20 minutes, three times per week for the next three months.
agree :___1__:___2__:___3__:___4__:___5__:___6__:___7___: disagree
Most people like me exercised for at least 20 minutes, three times per week in the three months following their major surgery.
unlikely :___1__:___2__:___3__:___4__:___5__:___6__:___7___: likely
4. Diet Supplements In UK Women
Use of dietary supplements among women over 40 in the UK is widespread, estimated at 1 in 6 being regular users. Despite this prevalence, very little research has been conducted to understand the underlying explanatory factors.
Conner et al. (2003) applied the theory of planned behavior to better understand this phenomenon. Over 300 supplement users and nonusers were administered a questionnaire that included theory of planned behavior questions and frequency of supplement use.
Sample items on the questionnaire (p. 1979) were as follows:
Past behavior: self-reported dietary supplement use
Intention: “I intend to take dietary supplements”
Overall attitude: “Overall, I think that my taking dietary supplements would be. . . good-bad”
Subjective norms: “People who are important to me would approve of my taking dietary supplements”
Perceived behavioral control: “If I wanted to, I could easily take dietary supplements”
Although the analyses were complex and exhaustive, the researchers summarize their findings:
“…the current findings do highlight the potential of the theory of planned behavior in exploring supplement-taking behavior while helping to elucidate those factors influencing an individual’s motivation to take supplements” (p. 1982).
5. Theory of Planned Behavior And E-Waste Recycling
The above video provides an excellent overview of research conducted on consumer determinants of electrical and electronic equipment (e-waste) recycling.
This is a fast-growing waste stream with a low recycling rate. The video identifies the specific domains of TBD that were the best predictors of e-waste recycling.
For instance, at 4:21, Figure 3a shows that 33% of the studies found that attitudes were the best predictors; 44% found subjective norms were the best predictors; and 22% found perceived behavioral control was the best predictor.
At 6:29, the chart displays the most influential theory of planned behavior domains that predict recycling behavior. Economic incentives were identified in 83% of the studies as the most influential factor, while knowledge of what, where, and how to recycle was identified in 77% of the studies as the most influential factor.
Both of these factors fall into the category of perceived behavioral control.
The video provides valuable insights regarding additional factors outside the theory of planned behavior model that may be influential in explaining e-waste recycling behavior.
Conclusion
The theory of planned behavior has been applied to explain a wide range of human behavior, from likelihood of exercising to engaging in environmentally friendly behavior such as recycling.
Although many studies have demonstrated the explanatory value of the model, no model is perfect. Human behavior is complex, multidimensional, and not always a result of reasoned action.
Therefore, this model has never been able to explain the actions under study with 100% accuracy.
To be fair, it is highly unlikely that a model that reaches such a degree of accuracy will ever be devised. In the meantime, this theory has proven to be quite useful and will improve as additional key factors are identified and incorporated.
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 (pp. 11-39). Berlin, Heidelber, New York: Springer-Verlag.
Ajzen, I. (1991). Theory of planned behavior. Organizational Behavior and Human Decision Processes, 50(2), 179–211.https://doi.org/0.1016/0749-5978(91)90020-T
Bosnjak, Michael & Ajzen, Icek & Schmidt, Peter. (2020). Theory of Planned Behavior: Selected Recent Advances and Applications. Europe’s Journal of Psychology, 16, 352-356. https://doi.org/10.5964/ejop.v16i3.3107
Godin, Gaston & Kok, Gerjo. (1996). Theory of Planned Behavior: A Review of Its Applications to Health-Related Behaviors. American Journal of Health Promotion, 11, 87-98. https://doi.org/10.4278/0890-1171-11.2.87
Reger, B., Cooper, L., Booth-Butterfield, S., Smith, H., Bauman, A., Wootan, M., et al. (2002). Wheeling walks: A community campaign using paid media to encourage walking among sedentary older adults. Preventive Medicine, 35, 285–292.
Hardeman, W., Johnston, M., Johnston, D. W., Bonetti, D., Wareham, N. J., & Kinmonth, A. L. (2002). Application of theory of planned behaviour change interventions: A systematic review. Psychology and Health, 17, 123-158.
Masud, M.M.; Al-Amin, A.Q.; Junsheng, H.; Ahmed, F.; Yahaya, S.R.; Akhtar, R.; Banna, H. (2016). Climate change issue and theory of planned behaviour: Relationship by empirical evidence. Journal of Cleaner Production, 113, 613–623.
Zobeidi, T., Yaghoubi, J. & Yazdanpanah, M. (2022). Exploring the motivational roots of farmers’ adaptation to climate change‑induced water stress through incentives or norms. Science Reports, 12, 15208. https://doi.org/10.1038/s41598-022-19384-1
Dr. Cornell has worked in education for more than 20 years. His work has involved designing teacher certification for Trinity College in London and in-service training for state governments in the United States. He has trained kindergarten teachers in 8 countries and helped businessmen and women open baby centers and kindergartens in 3 countries.
This article was peer-reviewed and edited by Chris Drew (PhD). The review process on Helpful Professor involves having a PhD level expert fact check, edit, and contribute to articles. Reviewers ensure all content reflects expert academic consensus and is backed up with reference to academic studies. Dr. Drew has published over 20 academic articles in scholarly journals. He is the former editor of the Journal of Learning Development in Higher Education and holds a PhD in Education from ACU.