Theory Of Planned Behavior (TPB)

Theory Of Planned Behavior (TPB)

Primary Disciplinary Field(s): Social Psychology, Health Psychology, Behavioral Economics
Proponents: Icek Ajzen

1. Core Principles

The Theory of Planned Behavior (TPB) is a powerful and widely utilized socio-psychological model designed to explain and predict deliberate human behaviors that individuals perceive they have the ability to control. Proposed by researcher Icek Ajzen, the theory suggests a strong link between an individual’s beliefs and their subsequent actions. The fundamental premise of the TPB is that the most direct determinant of actual behavior is the individual’s behavioral intention—the conscious plan or motivation to exert effort toward performing the behavior.

Behavioral intention, in turn, is shaped by a set of three conceptual predictors: the individual’s attitude toward the behavior, the perceived subjective norms, and the level of perceived behavioral control (PBC). The TPB moves beyond simple motivation, explicitly incorporating the concept of ability and control. It states that behavioral success depends not only on a person’s motivation to act but also on their perceived capacity to overcome potential barriers and successfully execute the action. If an individual harbors a strong intention to perform a behavior but lacks the necessary resources or skills, the TPB predicts that the intention may fail to translate into observable behavior.

2. Historical Development

The Theory of Planned Behavior was developed as a crucial refinement of its predecessor, the Theory of Reasoned Action (TRA). The TRA, proposed earlier by Ajzen and Martin Fishbein in 1967, was groundbreaking in its attempt to explain the systematic relationship between attitudes and behavior. The TRA posited that an individual’s behavioral intentions are formed by their attitude concerning the behavior and their perception of subjective norms, assuming that human beings are fundamentally rational decision-makers.

However, the TRA proved limited in its capacity to predict actions that were not entirely under the individual’s volitional control. Many complex, real-world behaviors—such as adhering to strict medication regimens, managing addiction, or securing stable employment—are often constrained by environmental, resource, or skill barriers. Recognizing this gap, Ajzen introduced the TPB in the mid-1980s by integrating the third key predictor: Perceived Behavioral Control. This addition significantly enhanced the model’s predictive power, making it applicable to a much broader range of behaviors, particularly those that require substantial planning, effort, and resources. The TPB is thus recognized as the standard model for behaviors where perceived control is a significant factor.

3. Key Concepts and Components

The TPB framework is built upon six interdependent factors that determine the likelihood of an individual forming a strong behavioral intention and successfully executing the corresponding behavior. These factors provide specific targets for interventions aimed at behavioral change.

• Attitude toward the Behavior: This component reflects the individual’s positive or negative evaluation of performing the behavior. It is formed by the individual’s behavioral beliefs—their assessment of the potential consequences (both positive and negative) resulting from the performance of the behavior, and the value placed on those predicted outcomes.
• Subjective Norms: This refers to the perceived social pressure to engage or not engage in a behavior. It is derived from normative beliefs, which are the perceived expectations of important reference groups (e.g., family, peers, social media), coupled with the individual’s willingness (motivation to comply) to adhere to these expectations.
• Behavioral Intention: Serving as the immediate antecedent of actual behavior, this is the motivational component that indicates how ready an individual is to perform a given behavior. It synthesizes the influence of attitude and subjective norms, mediated by perceived control.
• Perceived Behavioral Control (PBC): This critical factor is the perception of the ease or difficulty of performing the behavior, reflecting the degree of control the individual feels they possess. PBC is influenced by control beliefs—the perceived presence or absence of requisite resources and opportunities (e.g., time, money, skills).
• Perceived Power: This element, often considered part of PBC, relates specifically to the perceived impact of each control factor (facilitator or impediment). It involves judging the strength of a resource or barrier in affecting the successful completion of the action.
• Social Norms: While often grouped with subjective norms, recent applications of the TPB sometimes distinguish between injunctive norms (what others approve of, aligning with subjective norms) and descriptive norms (what others actually do), adding a layer of descriptive social influence that can significantly affect intention.

4. Applications and Examples

The Theory of Planned Behavior is one of the most widely applied frameworks in the applied social sciences, particularly in areas requiring prediction and explanation of complex voluntary actions. It is extensively used in health psychology to predict adherence to difficult regimens and to understand high-risk behaviors.

The theory is highly effective in predicting various health behaviors such as deciding to visit a healthcare provider, engaging in regular physical activity, decisions concerning substance use (including smoking and drinking), and compliance with medical recommendations. For instance, in predicting preventative behaviors like vaccination, researchers would measure the individual’s positive attitude toward the vaccine, the social pressure from family and media (subjective norms), and their perceived control (e.g., ease of access, appointment availability) to predict the intention to vaccinate.

Beyond clinical settings, the TPB has proven valuable in studying economic and environmental choices. Examples include predicting consumer decisions to purchase ethical or sustainable products, the intention of employees to follow new organizational policies, and the planning behind adopting new technologies. In the example provided by source material, a person planning to steal an item intends to act based on a positive outcome evaluation (attitude: getting money) and their perceived ability to execute the theft and subsequent sale (perceived behavioral control).

5. Criticisms and Limitations

While highly predictive, the TPB is subject to several academic critiques, primarily concerning its reliance on rational processing and its exclusion of certain behavioral determinants. A major criticism is that the model assumes that humans engage in detailed cognitive processing before every action, potentially overlooking behaviors that are habitual, spontaneous, or driven purely by emotion or impulse.

Furthermore, critics often point out that the predictive gap between intention and actual behavior remains significant, even with the inclusion of PBC. Intention is a dynamic psychological state that can change rapidly; therefore, the temporal stability of intention remains a challenge. Additionally, the TPB is sometimes criticized for being overly parsimonious, failing to integrate other relevant variables, such as moral obligation, anticipated regret, or descriptive social norms, which have been empirically shown to increase the model’s explanatory power when added as external variables. The overlap and conceptual redundancy between Perceived Behavioral Control and existing concepts like self-efficacy also remain points of discussion among researchers.

Further Reading

• Theory of Planned Behavior (Official Website by Icek Ajzen)
• Theory of Planned Behavior – Wikipedia
• Theory of Reasoned Action – Wikipedia