The theory of planned behavior (TPB) is one of a class of related theories of behavior change. The theory was developed by Icek Ajzen (1985, 1991) as an extension of the theory of reasoned action (TRA; Fishbein & Ajzen 1975), itself a model of behavior change. The TRA originated as a solution to the problem of attitude–behavior correspondence. In brief, the problem is the commonly observed fact that people can have attitudes toward a behavior that are favorable or unfavorable but not act on those attitudes in a consistent way.
Forerunner: The Theory Of Reasoned Action
To understand the importance of the TPB requires understanding of how the TRA solves the problem of attitude–behavior correspondence. As part of the solution, Martin Fishbein and Icek Ajzen introduced the concept of intention as a mediator of attitudes and behavior. When a behavior is under volitional control – that is, when a person can readily enact a behavior or not – then the intention to carry out such a (volitional) action will lead to that behavior under certain circumstances. The TRA initially is restricted to volitional behaviors with behavioral intentions mediating attitudes and behavioral response.
To insure correspondence among attitudes, behavioral intention, and behavior requires behaviors that are carefully defined and that there is correspondence across the three. The behavior must first be well defined. For example, losing weight is not a behavior – it is, instead, a goal. The goal of losing weight might be achieved in many different ways, such as “my exercising vigorously at the gym for 30 minutes three times per week starting this week.” Definitional correspondence requires matching in time, action, context, and target. The action is exercising vigorously for 30 minutes three times per week; the time is this week; the context is “at the gym”; the target is my behavior, not the value of people exercising more generally. By defining behaviors precisely and not confusing behavior with general goals, intentions can be defined precisely. When matched in this level of specificity, behavior and intention will tend to correlate strongly.
This fundamental development in the conceptualization and measurement of behavior along with the introduction of a corresponding conceptualization of behavioral intention sets the stage for the solution of the problem of attitude–behavior correspondence by inserting behavioral intention between attitude and behavior. The TRA then turns its attention to accounting for behavior by accounting for behavioral intention.
In the TRA, behavioral intention is determined by two broad factors – cognitive and social. Cognitive factors are attitudes toward the behavior, again carefully matched in level of specificity to maximize the association with intentions to carry out the behavior. Social normative factors are the perceived pressures that a person feels from significant others to engage in the behavior. These two classes of predictors are the attitudinal and social normative routes to the formation of intention.
The chief conclusion from the TRA, the core for the more general TPB, is that attitudes toward the behavior and social normative pressure will predict behavioral intention and ultimately behavior when the behavior is well defined and when the theory’s concepts are matched in level of specificity. Cumulative studies of the associations between attitudes and behavioral intention and between behavioral intention and behavior show considerable consistency when there is a match in level across concepts (Kim & Hunter 1992).
The attitudinal and social normative routes to intention in turn employ subjective expected utility functions from economics and the psychology of decision-making (Arrow 1951) to account for attitude toward the behavior and for social normative pressure. Specifically, attitudes, and perceived social norms are, themselves, functions of underlying beliefs – about the outcomes of performing the behavior in question, and about the normative expectations of specific referent groups. Thus, for example, the more one believes that performing the behavior in question will lead to “good” outcomes and prevent “bad” outcomes, the more favorable is one’s attitude toward performing the behavior.
Similarly, the more one believes that specific others think one should (or should not) perform the behavior in question, and the more one is motivated to comply with those specific others, the more social pressure one will feel (or the stronger the subjective norm) with respect to performing (or not performing) the behavior.
Developing Into The Theory Of Planned Behavior
The New Element
The core of the TPB is the TRA. The TRA assumes that behavior is the result of the information people have – correct or incorrect – about good and bad consequences of the behavior for themselves and what others think they should do.
As a theory of volitional behavior, the TRA focuses on behaviors that are under the control of actors through their own agency. For example, exercising at the gym tonight is generally under a person’s control and so is volitional. However, if the person requires transportation to the gym and their car is in the mechanic’s shop, then the intention to go to the gym depends on factors outside of the person’s immediate control. Although walking and mass transit are possibilities, they erect barriers to the realization of intention. The behavior is no longer completely under volitional control but depends in part on the perception of how controllable the behavior is.
The TPB holds to the core of the TRA but extends it to include perceived behavioral control as a predictor of behavioral intention parallel to the attitudinal and social normative routes. Perceived behavioral control is how easy or difficult the performance of the behavior is perceived to be. Perceived behavioral control is related to the concept of self-efficacy introduced by Bandura (1977) and is also a measure of the available resources, opportunities, and skills necessary to undertake a behavior. Perceived behavioral control functions as a predictor of both intention and behavior within the TPB and, like attitudes and subjective norms in the TRA, is itself a function of control beliefs and the perceived power of those beliefs to affect the outcome. So, even if I believe that going to the gym regularly and exercising will improve my physical appearance and believe that my significant others want me to go to the gym regularly, perceived difficulties with mass transit may lead me to avoid the gym, marking this behavior as less under volitional control. Research summaries in various contexts have shown that perceived behavioral control adds substantial explanatory power to the prediction of behavioral intention (Ajzen & Albarracin 2007).
Two characteristics of a consequential theory are its ability to predict and its generative capacity. The TPB and its variants – including the TRA and the integrated model of behavior change (Fishbein 2000) – have generated thousands of published studies in their 35-year history. These studies have focused on topics as diverse as politics, consumer behavior, exercise, safe sex practices, smoking, video games, and shoplifting, among many others (Eagley & Chaiken 1993; Ajzen & Fishbein 2005). The TPB has been a rich theory for researchers, having wide applicability in diverse contexts.
The theory has also been powerful in its ability to predict behavior. As Ajzen noted in a reflection on the theory’s origins (Ajzen & Albarracin 2007), it was designed in part to move beyond the weak predictive capacity of dispositional theories in psychology. When the theory is implemented appropriately, substantial variation in intention is explained by the three routes to behavioral intention even in special populations (e.g., adolescents) and with socially undesirable behaviors (e.g., drug use intention).
Applicability In Communication
The TPB and its variants are theories of behavior change but have considerable influence in research problems in communication and persuasion. They help campaign designers answer the question: “What approaches, topics, and beliefs should my campaign messages target?” The three routes to behavioral intention identify three different ways that persuasion can occur – by manipulating attitudes, social norms, or perceived behavioral control. In turn, these components are based on underlying behavioral beliefs, normative beliefs, and control beliefs that can be targeted in the design of persuasive messages. Which route to choose in a particular case and which beliefs to target depend on conducting formative research with the behavior and with the target population.
In addition to locating the possible routes to persuasion for the given behavior and target population, the TPB also suggests that specific beliefs or particular routes to persuasion can be made more salient by communication campaigns that target those beliefs (Cappella et al. 2003; Fishbein & Yzer 2003). The TPB does not assume that the three routes to persuasion are equally strong. Communication campaigns can emphasize one route to intention rather than another or one behavioral belief rather than another in order to make it more salient. If a campaign primes a route or belief, then that component could play a stronger role in subsequent behavioral intention by having a greater weight during decision-making (Fishbein & Yzer 2003). Thus, the TPB guides communication campaigns and persuasion in two important but complementary ways – persuasion that changes a belief and priming, which makes a belief more cognitively salient.
The TPB and its variants guide researchers to routes to persuasion and to beliefs to target in persuasive efforts but they do not tell us how to design messages or other interventions to achieve these changes. Other theories complementary to the TPB need to be consulted in the message design phase (Cappella 2006). In this sense, the TPB does not compete with theories of attitude change (e.g., the elaboration likelihood model) or with information processing theories but answers questions about behavior change that these theories are not able to ask.
A theory as productive and time-tested as the TPB is not without its criticisms. These have included the role of affect, causality, sufficiency, habit and past behavior, the nature of the routes to intention, and rationality. These issues are summarized in Eagley and Chaiken (1993) and considered in several other places (Ajzen & Fishbein 2005; Fishbein 2007). Even if one acknowledges some theoretical challenges, the TPB and its cousins have had profound effects on the study of human behavior and on the design of communication campaigns and interventions. Few theories have had the staying power, influence, and predictive success of the TPB.
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