Theory of Planned Behavior Definition
Developed by Icek Ajzen in 1985, the theory of planned behavior (TPB) is today perhaps the most popular social-psychological model for the prediction of behavior. It has its roots in Martin Fishbein and Ajzen’s theory of reasoned action, which was developed in response to observed lack of correspondence between general dispositions, such as racial or religious attitudes, and actual behavior. Instead of dealing with general attitudes of this kind, the TPB focuses on the behavior itself and goes beyond attitudes to consider such other influences on behavior as perceived social norms and self-efficacy beliefs.
Theory of Planned Behavior Conceptual Framework
According to the theory, human social behavior is guided by three kinds of considerations: beliefs about the behavior’s likely positive and negative outcomes, known as behavioral beliefs; beliefs about the normative expectations of others, called normative beliefs; and beliefs about the presence of factors that may facilitate or impede performance of the behavior, termed control beliefs. For example, people may believe that the behavior of exercising, among other things, improves physical fitness and is tiring (behavioral beliefs), that their family and friends think they should exercise (normative beliefs), and that time constraints make it difficult to exercise (control belief). Taken together, the total set of behavioral beliefs produces a favorable or unfavorable attitude toward the behavior; the total set of normative beliefs results in perceived social pressure to perform or not to perform the behavior, or subjective norm; and, in their totality, control beliefs give rise to a sense of self-efficacy or perceived control over the behavior.
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Attitude toward the behavior, subjective norm, and perceived behavioral control jointly lead to the formation of a behavioral intention. The relative weight or importance of each of these determinants of intention can vary from behavior to behavior and from population to population. However, as a general rule, the more favorable the attitude and subjective norm are, and the greater the perceived behavioral control is, the stronger is the person’s intention to perform the behavior in question. Finally, people are expected to carry out their intentions when the appropriate opportunity arises. However, successful performance of a behavior depends not only on a favorable intention but also on a sufficient level of volitional control, that is, on possession of requisite skills, resources, opportunities, and the presence of other supportive conditions. Because many behaviors pose difficulties of execution, the TPB adds perceived behavioral control to the prediction of behavior. To the extent that perceived behavioral control is accurate, it can serve as a proxy of actual control and can, together with intention, be used to predict behavior.
Beliefs play a central role in the TPB, especially those salient behavioral beliefs that are most readily accessible in memory. In applications of the theory, these salient beliefs are elicited in a free-response format by asking a representative sample of respondents to list the advantages and disadvantages of performing a behavior of interest (behavioral beliefs), to list the individuals or groups who approve or disapprove of performing the behavior (normative beliefs), and to list the factors that facilitate or inhibit performance of the behavior (control beliefs). The most frequently emitted behavioral, normative, and control beliefs are assumed to be the salient beliefs in the population and to determine prevailing attitudes, subjective norms, and perceptions of behavioral control. These salient beliefs are focused on the particular behavior of interest, and they serve as the fundamental explanatory constructs in the theory. More general factors, such as personality traits, gender, education, intelligence, motivation, or broad values are assumed to influence behavior only indirectly by their effects on salient beliefs. Assume, for example, that women are found to drink less alcohol than men. The TPB would explain this gender effect by predicting that men hold more favorable behavioral, normative, or control beliefs about drinking than women do.
The TPB assumes that human social behavior is reasoned or planned in the sense that people are assumed to take into account a behavior’s likely consequences, the normative expectations of important referents, and factors that may impede performance of the behavior. Although the beliefs people hold may sometimes be inaccurate, unfounded, or biased, their attitudes, subjective norms, and perceptions of behavioral control are thought to follow spontaneously and reasonably from these beliefs, to produce a corresponding behavioral intention, and ultimately to result in behavior that is consistent with the overall tenor of the beliefs. This does not necessarily presuppose a deliberate, effortful retrieval of information and construction of attitudes prior to every enactment of a behavior. After at least minimal experience with the behavior, attitude, subjective norm, and perceived behavioral control are assumed to be available automatically as performance of the behavior is contemplated.
Successful application of the TPB is predicated on two conditions. First, the measures of attitude, subjective norm, perceived behavioral control, and intention must be compatible with one another and with the measure of behavior relative to the action involved, the target at which the action is directed, and the context and time of its enactment. Second, attitude, subjective norm, perceived behavioral control, and intention must remain relatively stable over time. Any changes in these variables prior to observation of the behavior will tend to impair their predictive validity.
Empirical Support for Theory of Planned Behavior
The TPB has been applied in research on a great variety of behaviors, including investment decisions, high-school dropout, mountain climbing, driving violations, recycling, class attendance, voting in elections, extramarital affairs, antinuclear activism, playing basketball, choice of travel mode, tax evasion, and a host of other activities related to protection of the environment, crime, recreation, education, politics, and religion. It has found its most intense application, however, in the health domain, where it has been used to predict and explain such varied behaviors as drinking, smoking, drug use, exercising, blood donation, dental care, fat consumption, breast self-examination, condoms use, weight loss, infant sugar intake, getting medical checkups, physician referrals, protection of the skin from the sun, living kidney donation, and compliance with medical regimens. The results of these investigations have, by and large, confirmed the theory’s structure and predictive validity, especially when its constructs were properly assessed. Even without this caveat, the TPB has fared very well. Meta-analytic reviews of close to 200 data sets in a variety of behavioral domains have found that the theory accounts, on average, for about 40% of the variance in intentions, with all three predictors—attitude toward the behavior, subjective norm, and perceived behavioral control—making independent contributions to the prediction; the reviews also found that intentions and perceptions of behavioral control explain about 30% of the behavioral variance.
Given its predictive validity, the TPB can serve as a conceptual framework for persuasive messages and other interventions designed to influence intentions and behavior. Influence attempts directed at one or more of the theory’s predictors have been found to increase use of public transportation among college students, to raise the effectiveness of job search behavior of unemployed individuals, to promote testicular self-examination among high-school and college students, and to induce alcoholics to join a treatment program.
Intention-Behavior Relation in Theory of Planned Behavior
For the TPB to afford accurate prediction, intentions must remain relatively stable prior to observation of the behavior. Empirical evidence supports this expectation, showing that the intention-behavior relation declines with instability in intentions over time. More important, the theory also assumes that people will act in accordance with their intentions under appropriate circumstances. This expectation has frequently been challenged, beginning with R. T. LaPiere’s classic study in which ready acceptance of a Chinese couple in hotels, motels, and restaurants contrasted sharply with stated intentions not to accept “members of the Chinese race” in these same establishments. Similar discrepancies have been revealed in investigations of health behavior where it is found that large proportions of participants fail to carry out their intentions to use condoms, to undergo cancer screening, to exercise, to perform breast self-examination, to take vitamin pills, to maintain a weight-loss program, and so forth.
A variety of factors may be responsible for observed failures of effective self-regulation, yet a simple procedure can often do much to reduce the gap between intended and actual behavior. When individuals are asked to formulate a specific plan—an implementation intention—indicating when, where, and how they will carry out the intended action, the correspondence between intended and actual behavior often increases dramatically. Behavioral interventions of this kind that focus on implementation intentions have been shown to produce high rates of compliance with such recommended practices as cervical cancer screening and breast self-examination.
Theory of Planned Behavior Critiques
Although popular and successful, the TPB has not escaped criticism. One type of critique has to do with the theory’s sufficiency—the proposition that attitudes, subjective norms, and perceptions of behavioral control are sufficient to predict intentions and behavior. Investigators have suggested a number of variables that might be added to the theory to improve its predictive validity. Among the proposed additions are desire and need, affect and anticipated regret, personal and moral norms, past behavior, and self-identity (i.e., the extent to which people view themselves as the kind of person who would perform the behavior in question).
In another major critique, investigators have challenged the theory’s reasoned action assumption, or more precisely, they have argued that reasoned action may represent only one mode of operation, the controlled or deliberate mode. According to Russell Fazio’s MODE model, reasoned action occurs when people are motivated and capable of retrieving their beliefs, attitudes, and intentions in an effortful manner. When they lack motivation or cognitive capacity to do so, they are said to operate in the spontaneous mode where attitudes must be strong enough to be activated automatically if they are to guide behavior.
A related critique of the TPB’s reasoned action assumption relies on the well-known phenomenon that, with repeated performance, behavior becomes routine and no longer requires much conscious control for its execution. Some have suggested that as a result of this process of habituation, initiation of the behavior becomes automatic, and control over the behavior is transferred from conscious intentions to critical stimulus cues. The finding that frequency of past behavior is often a good predictor of later behavior and, indeed, that it has a residual impact on later behavior over and above the influence of intention and perceived behavior control, has been taken as evidence for automaticity in social behavior.
- Ajzen, I., & Fishbein, M. (2005). The influence of attitudes on behavior. In D. Albarracin, B. T. Johnson, & M. P. Zanna (Eds.), The handbook of attitudes (pp. 173-221). Mahwah, NJ: Erlbaum.