Theory of Planned Behavior (TPB)

The Theory of Planned Behavior (TPB) is a socio-psychological model designed to predict human behavior, starting from the premise that individual actions are not always fully governed by rational judgment or volition (Ajzen & Madden, 1986). This theory reflects the complexity of human behavior, considering that specific actions are not merely dependent on personal intention or determination but are also influenced by external constraints and situational factors.

The TPB complements the unrealistic assumption that individuals can completely control their behavior through willpower alone. Instead, it aims to explain and predict human actions more accurately by systematically analyzing the psychological, social, and environmental factors influencing behavior. Through this integrated approach, TPB seeks to provide a comprehensive and realistic understanding of human behavior.

To explain the process of behavior formation and execution, the TPB systematically analyzes psychological and social factors, centering on three core components: attitude toward behavior, subjective norm, and perceived behavioral control.

This theory is widely applied in explaining and predicting human actions within various social and environmental contexts. It is particularly instrumental in addressing practical issues such as health behavior, environmental conservation, and consumer behavior, contributing to research and intervention programs aimed at solving real-world problems.

1. Background and Theoretical Foundations

The understanding and prediction of human behavior have long been subjects of interest in psychology and sociology. Early research emphasized attitudes (Attitude) as a primary determinant of behavior, viewing them as the sole factor in decision-making. This traditional approach posited that internal beliefs and values directly shaped behavior. However, over time, inconsistencies in the relationship between attitudes and actions were revealed, highlighting the limitations of this perspective.

For instance, individuals who positively evaluate environmental protection may not always engage in recycling, demonstrating the need to consider a broader range of factors influencing behavior.

Against this backdrop, Fishbein and Ajzen (1975) proposed the Theory of Reasoned Action (TRA) to provide a more sophisticated explanation of the relationship between attitudes and behavior. The TRA introduced behavioral intention as a mediating variable, suggesting that actions are not solely determined by attitudes but by an individual's will to perform a specific behavior. Behavioral intention is influenced by two primary factors:

Attitude toward behavior: The positive or negative evaluation of a specific action.
Subjective norm: The perceived expectations of significant others and the motivation to meet those expectations.

The TRA emphasized behavioral intention as the primary predictor of action, highlighting that human behavior results from the interplay between personal attitudes and social expectations.

However, the TRA assumed that individuals have complete control over their actions, failing to account for external constraints such as environmental factors or resource limitations. For example, a person strongly intending to quit smoking may still fail to do so due to social influences or stress, illustrating a gap between intention and behavior.

To address these limitations, Ajzen (1985) extended the TRA by introducing the Theory of Planned Behavior (TPB). This model added perceived behavioral control as a new variable to enhance its predictive accuracy.

Perceived behavioral control reflects an individual’s confidence in their ability to successfully perform a specific action, encompassing the perceived availability of resources and opportunities. It influences not only behavioral intention but also directly affects behavior. By incorporating this factor, the TPB offers a comprehensive framework that integrates internal and external influences on behavior formation and execution.

The introduction of the TPB marked a significant advancement in understanding human behavior. While the TRA focused on attitudes and subjective norms to predict behavioral intention, the TPB expanded this framework to include perceived behavioral control, thereby increasing the model's validity and scope. This innovation underscored the interaction between psychological and environmental factors, contributing to a more refined explanation of human behavior.

2. Key components of theory of Planned Behavior

(1) Attitude toward the Behavior

Attitude toward the behavior refers to an individual’s tendency to evaluate a specific action positively or negatively, and it is considered one of the key determinants of behavioral intention (Ajzen & Fishbein, 1980). Attitudes toward a behavior are formed through the individual’s expectations of the behavior’s outcomes and their evaluation of those outcomes. The more strongly an individual believes that a behavior will lead to positive outcomes, the more favorable their attitude toward that behavior will be (Ajzen, 1991). Conversely, if a behavior is perceived to result in negative outcomes, the individual will likely hold a negative attitude toward it. Thus, attitudes serve as a critical indicator for predicting the direction of behavior.

Unlike beliefs, which are purely informational, attitudes incorporate emotional elements. According to Ajzen (2002), behavioral beliefs shape attitudes by linking specific behaviors to expected outcomes. For example, when an individual strongly believes that a specific behavior will produce positive results, their attitude toward that behavior is more likely to be favorable. Costello and Zalkind (1963) highlighted that attitudes are influenced not only by individual beliefs but also by social factors such as family, peer groups, and culture. This demonstrates that attitudes are shaped by both internal beliefs and external environmental factors.

Attitudes are influenced by a variety of factors, including behavioral complexity, individual tendencies, and societal benefits. Even if a behavior is challenging to perform, individuals may develop a positive attitude if they perceive significant benefits from the behavior. Consequently, attitudes reflect a complex judgment of behavioral outcomes rather than simple personal preferences. Once formed, attitudes tend to be stable and resistant to change. For instance, individuals with positive attitudes toward healthy lifestyles are more likely to engage in health-promoting behaviors, such as regular exercise.

Ajzen and Fishbein (1980) emphasized that attitudes are a significant antecedent of behavioral intention. Behavioral intention refers to an individual’s determination to perform a specific action, and attitudes are a critical factor in shaping this determination. Attitudes and behavioral intentions are functionally related, with positive attitudes enhancing behavioral intentions (Ajzen, 1991). For example, individuals who believe that a behavior will lead to favorable outcomes and hold a positive attitude toward it are more likely to form strong intentions to perform the behavior. Conversely, when a behavior is evaluated negatively, behavioral intentions are likely to weaken.

Attitudes influence behavior indirectly through their impact on behavioral intentions rather than directly determining behavior (Ajzen & Fishbein, 1980). This suggests that while attitudes play a pivotal role in the decision-making process, they are not the sole determinant of behavior. Therefore, positive attitudes toward a behavior increase the likelihood of strong behavioral intentions, which, in turn, influence the performance of the behavior. For example, individuals with favorable attitudes toward environmental protection are more likely to engage in environmentally responsible behaviors, such as recycling. In this way, attitudes provide critical insights for understanding and predicting human behavior.

In conclusion, attitudes toward behavior play a vital role in shaping behavioral intentions and influencing behavior. They go beyond mere beliefs by incorporating emotional, personal, and social factors, and they form the basis for evaluating and expressing preferences toward specific actions. These attitudes serve as an essential foundation for designing behavioral change programs or policies aimed at predicting behavior. Therefore, attitudes are an indispensable component for understanding the complexity of human behavior and play a central role in the Theory of Planned Behavior.

Components of Attitude Formation:

Belief about Outcomes: The individual’s expectations regarding the outcomes of a specific behavior.
Evaluation of Outcomes: The extent to which the individual values those outcomes.

For example, believing that daily exercise improves health (positive expectation) and highly valuing health can contribute to a positive attitude toward exercise.

Significance:

Positive attitudes are strongly correlated with higher behavioral intentions.
However, attitudes alone may not suffice to predict behavior, highlighting the importance of interactions with other factors.

(2) Subjective Norm

Subjective norm refers to an individual’s perception of social pressure to perform or refrain from a specific behavior, including their motivation to comply with others’ expectations (Ajzen, 1991). It encompasses how the individual perceives significant others’ evaluations of their behavior and their motivation to meet those expectations (Lee et al., 2013). For example, the higher the expectations of close individuals such as family, friends, and colleagues, the more likely the individual is to perform the behavior. Conversely, the presence of negative expectations may reduce the likelihood of the behavior (Fishbein & Ajzen, 1980).

According to Ajzen (2002), normative beliefs about others' expectations shape subjective norms. These norms consist of normative beliefs about social expectations and the individual’s motivation to comply with them (Kwak, 2012; Ajzen, 1985). Normative beliefs refer to the individual’s perception of whether significant referents (e.g., family, friends) would approve or disapprove of their behavior, acting as a source of perceived social pressure (Ajzen & Madden, 1986). Therefore, if significant others exhibit a positive attitude toward a specific behavior, the likelihood of performing that behavior increases. Conversely, negative attitudes from these referents decrease the likelihood of performing the behavior.

Subjective norms can be understood as the social norms and pressures experienced by individuals as members of a community (Son & Lee, 2010). These norms are shaped by the expectations of referents and the individual’s motivation to meet those expectations. For instance, if an individual strongly believes that a behavior will be positively evaluated by family or colleagues, they are more likely to perform that behavior. Thus, subjective norms play a critical role in shaping behavioral intention, helping predict whether an individual will perform a specific action (Ajzen, 1991).

In the Theory of Planned Behavior (TPB), subjective norm is a significant variable because individuals are more likely to act in accordance with the expectations of people they consider important. For example, if a person perceives that their close family members support a behavior, they are more inclined to perform that behavior to meet those expectations.

Fishbein and Ajzen (1980) emphasized that when referents important to the individual express a positive attitude toward a behavior, the likelihood of performing that behavior increases. Conversely, negative attitudes from referents reduce the likelihood of the behavior. This indicates that behavior is influenced not only by internal attitudes and intentions but also by the expectations and support of others in the social context.

In conclusion, subjective norm is a critical social factor in the decision-making process, playing a central role in shaping behavioral intention. It includes social pressure from significant others such as family, friends, and colleagues, whose expectations and attitudes directly influence behavioral intention. As such, subjective norm is an essential element for understanding the social dimensions of human behavior and serves as a key predictor in the Theory of Planned Behavior.

Components of Subjective Norm:

Normative Beliefs: An individual’s belief about whether significant others would approve or disapprove of their behavior.
Motivation to Comply: The individual’s motivation to align with others’ expectations.

For example, if friends and family support quitting smoking and the individual feels motivated to meet these expectations, their intention to quit smoking is likely to strengthen.

Role of Social Pressure:

Subjective norms reflect the influence of relationships with significant others (e.g., family, friends, colleagues) and play a vital role in shaping behavioral norms within specific social environments.

(3) Perceived Behavioral Control

Perceived behavioral control refers to an individual’s subjective assessment of their ability and resources to perform a specific behavior. It is a critical variable in the Theory of Planned Behavior (TPB), as it directly influences both behavioral intention and behavior (Ajzen, 1991). According to Ajzen (2002), beliefs about factors that facilitate or hinder behavior shape perceived behavioral control. This perception is influenced by both internal factors, such as personality, skills, and abilities, and external factors, such as time, resources, and opportunities. These factors can either facilitate or obstruct behavior. When individuals cannot control these factors, they may act as barriers to performing the behavior.

Control beliefs refer to beliefs about the presence of factors that facilitate or hinder behavior. These beliefs contribute to perceived control and determine the ease or difficulty of performing the behavior based on the availability of necessary resources and opportunities. For example, individuals with sufficient skills and abilities are likely to find a behavior easier to perform, whereas a lack of time or resources may make the behavior more challenging. Ajzen and Driver (1992) suggested that these control beliefs act as factors that either promote or inhibit behavior, with perceived power over these factors determining the strength of perceived behavioral control.

Bandura (1977) introduced a concept similar to perceived behavioral control: self-efficacy, which refers to an individual’s belief and confidence in their ability to successfully perform a specific behavior. Self-efficacy represents the extent to which individuals perceive themselves as capable of executing the necessary actions. It is closely related to perceived behavioral control in the TPB. Ajzen and Fishbein (1980) noted that perceived behavioral control encompasses an individual’s perception of the availability of essential resources and opportunities required for behavior. Individuals with high self-efficacy are more likely to feel confident in their ability to control behavioral outcomes, which strengthens both behavioral intention and actual behavior.

Perceived behavioral control reflects personal beliefs about the ease or difficulty of performing a behavior. It influences not only behavioral intention but also directly impacts behavior itself (Ajzen, 1991). For example, when individuals believe they can control a specific behavior, their behavioral intentions are reinforced, increasing the likelihood of performing the behavior. Conversely, when individuals perceive the behavior as outside their control, their intentions weaken, and they are more likely to avoid the behavior (Terry & O’Leary, 1995). Additionally, unexpected challenges during the execution process may render a behavior impossible, even if behavioral intention has been formed. This highlights the importance of perceived behavioral control in realistically assessing behavioral feasibility and concretizing behavioral intentions.

Schifter and Ajzen (1985) explained that individuals with positive attitudes and subjective norms toward a specific behavior tend to have stronger perceived control, leading to greater behavioral intention. For instance, individuals with sufficient technical skills and access to supportive environmental resources are more likely to evaluate their ability to perform the behavior positively and strengthen their intentions to act. Conversely, a lack of resources or opportunities or significant technical challenges may reduce the likelihood of performing the behavior and weaken behavioral intentions.

In conclusion, perceived behavioral control is determined by both internal factors (e.g., personality, skills, abilities) and external factors (e.g., time, opportunities, resources). It is a crucial variable influencing both behavioral intention and actual behavior. The stronger the belief in their ability to control a specific behavior, the higher the likelihood of performing the behavior. Conversely, the perception of a lack of control reduces behavioral likelihood. Therefore, in the TPB, perceived behavioral control is considered a vital element for predicting behavioral success and serves as a foundational factor in designing behavioral change programs or policies.

Components of Perceived Behavioral Control:

Control Beliefs: Awareness of factors that facilitate or hinder behavior.
Perceived Ease or Difficulty: Assessment of how external conditions make behavior easier or more challenging.
- Example: Wanting to recycle but lacking access to nearby recycling facilities can restrict the likelihood of performing the behavior.
Connection with Self-Efficacy: Inspired by Albert Bandura’s concept of self-efficacy, which emphasizes the influence of confidence in one’s abilities on behavioral performance.

3. Overall Structure of the Theory of Planned Behavior

The three core components of the Theory of Planned Behavior (attitude, subjective norm, and perceived behavioral control) interact to form behavioral intention, which serves as the most significant antecedent for actual behavior. The structure can be illustrated as follows:

Attitude, Subjective Norm, Perceived Behavioral Control → Behavioral Intention → Actual Behavior
Perceived Behavioral Control → May also directly influence actual behavior

Behavioral Intention

Behavioral intention is a core component of the Theory of Planned Behavior, representing the subjective tendency and likelihood of an individual to perform a specific behavior. It indicates the direction of behavior before the actual decision and is influenced by attitude, subjective norm, and perceived behavioral control (Ajzen, 2002). By measuring the strength of an individual’s willingness or belief to execute a behavior, the likelihood of the behavior occurring can be predicted.

Ajzen (2005) defined behavioral intention as a mediating variable between attitude and behavior, describing it as a subjective state that connects attitudes to behavior. In the Theory of Planned Behavior, specific behaviors are assumed to be realized through behavioral intention. This highlights the importance of intention as a mediator in predicting behavior. For example, when positive attitudes, favorable subjective norms, and strong perceived behavioral control are present, behavioral intention is strengthened, increasing the likelihood of the behavior being performed.

However, behavioral intention does not always guarantee the execution of a behavior (Ajzen, 1991, 1985). Intentions may change over time, and shorter time intervals improve the accuracy of behavior prediction. For behavioral intention to be a reliable predictor of behavior, factors such as the stability of intention, passage of time, new information, and unexpected events must be controlled (Park, 2007). Thus, behavioral intention is regarded as the immediate determinant of behavior and plays a critical role in behavior prediction (Ajzen & Fishbein, 1980).

In the Theory of Planned Behavior, behavioral intention reflects the perceived strength of planning to execute a behavior. It acts as a major determinant of behavioral change. Attitude, subjective norm, and perceived behavioral control are antecedents of behavioral intention. Positive expectations about behavior enhance intention and increase the likelihood of the behavior, while negative expectations weaken intention and reduce the probability of action (Ajzen, 1991). For example, if an individual anticipates positive outcomes from a behavior, they are more likely to engage in it. Conversely, if negative outcomes are expected, intention to engage in the behavior weakens.

In conclusion, behavioral intention is the most important variable for predicting specific behaviors and serves as an immediate determinant of behavior. It reflects an individual’s willingness and belief in performing a specific behavior and is shaped by factors such as attitude, subjective norm, and perceived behavioral control. The Theory of Planned Behavior regards behavioral intention as the strongest predictor of action and an essential element for understanding behavior change and motivation.

Behavior

Behavior encompasses a wide range of mental, physical, and social activities. In the Theory of Planned Behavior, it is defined as an observable response by an individual in a given situation (Fishbein & Ajzen, 1977). Behavior is assumed to be directly influenced by the interaction of behavioral intention and perceived behavioral control. Positive intention is more likely to translate into behavior when there is strong perceived control over the action (Ajzen, 1991). The Theory of Planned Behavior focuses not only on predicting actions that are within the individual’s control but also on explaining behaviors under situations of limited control.

Behavior is defined as specific, observable actions performed in particular situations and can be understood as the process of predicting or realizing expected future actions. For example, behaviors like running, speaking, and walking can be externally observed, while emotions like joy, sadness, and resentment are internal and less directly observable (Spiegler & Guevremont, 2003). Thus, behavior is not limited to physical activities but also includes psychological and emotional responses.

The purpose of behavior can involve planned and goal-oriented actions, as well as habitual activities. For example, studying for academic achievement is goal-oriented behavior, while unconscious, repetitive actions are considered habitual behaviors. Ajzen (1985) explained that behavior may sometimes be under the individual’s partial control or entirely difficult to manage, and this control level plays a critical role in determining whether the behavior is performed. Behavior is viewed as occurring on a continuum rather than within strict boundaries.

In the Theory of Planned Behavior, behavior results from the interaction of behavioral intention and perceived behavioral control. This distinguishes it from the Theory of Reasoned Action, which focuses on behaviors that are fully within the individual’s control. The Theory of Planned Behavior extends this framework to include actions that may be partially beyond the individual’s control (Ajzen, 1991). For example, when a behavior is influenced by external factors (time, resources, environment) or internal factors (skills, psychological state), the Theory of Planned Behavior integrates these constraints into its predictive model.

In conclusion, behavior is the outcome of an individual’s intention and perceived control, emerging from the interaction of personal and environmental factors. The Theory of Planned Behavior explains these complex interactions, providing a useful framework for understanding and predicting individual actions. It encompasses both voluntary and involuntary behaviors, offering valuable theoretical support for designing behavior change programs and policies.

reference

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