Theory of Planned Behaviour

In psychology, the theory of planned behaviour (abbreviated TPB) is a theory that links one’s beliefs and behaviour.

The theory states that intention toward attitude, subject norms, and perceived behavioural control, together shape an individual’s behavioural intentions and behaviours.

The concept was proposed by Icek Ajzen to improve on the predictive power of the theory of reasoned action by including perceived behavioural control. It has been applied to studies of the relations among beliefs, attitudes, behavioural intentions and behaviours in various fields such as advertising, public relations, advertising campaigns, healthcare, sport management and sustainability.

Concepts of key variables

Normative beliefs and subjective norms

• Normative belief: an individual’s perception of social normative pressures, or relevant others’ beliefs that they should or should not perform such behaviour.
• Subjective norm: an individual’s perception about the particular behaviour, which is influenced by the judgment of significant others (e.g., parents, spouse, friends, teachers).

Control beliefs and perceived behavioural control

• Control beliefs: an individual’s beliefs about the presence of factors that may facilitate or hinder performance of the behaviour. The concept of perceived behavioural control is conceptually related to self-efficacy.
• Perceived behavioural control: an individual’s perceived ease or difficulty of performing the particular behaviour. It is assumed that perceived behavioural control is determined by the total set of accessible control beliefs.

Behavioural intention and behaviour

• Behavioural intention: an indication of an individual’s readiness to perform a given behaviour. It is assumed to be an immediate antecedent of behaviour. It is based on attitude toward the behaviour, subjective norm, and perceived behavioural control, with each predictor weighted for its importance in relation to the behaviour and population of interest.
• Behaviour: an individual’s observable response in a given situation with respect to a given target. Ajzen said a behaviour is a function of compatible intentions and perceptions of behavioural control in that perceived behavioural control is expected to moderate the effect of intention on behaviour, such that a favorable intention produces the behaviour only when perceived behavioural control is strong.

Conceptual / operational comparison

Perceived behavioural control vs. self-efficacy

As Ajzen (1991) stated in the theory of planned behaviour, knowledge of the role of perceived behavioural control came from Bandura’s concept of self-efficacy. More recently, Fishbein and Cappella stated[16] that self-efficacy is the same as perceived behavioural control in his integrative model, which is also measured by items of self-efficacy in a previous study.

In previous studies, the construction and the number of item inventory of perceived behavioural control have depended on each particular health topic. For example, for smoking topics, it is usually measured by items such as “I don’t think I am addicted because I can really just not smoke and not crave for it,” and “It would be really easy for me to quit.”

The concept of self-efficacy is rooted in Bandura’s social cognitive theory. It refers to the conviction that one can successfully execute the behaviour required to produce the outcome. The concept of self-efficacy is used as perceived behavioural control, which means the perception of the ease or difficulty of the particular behaviour. It is linked to control beliefs, which refers to beliefs about the presence of factors that may facilitate or impede performance of the behaviour.

It is usually measured with items which begins with the stem, “I am sure I can … (e.g., exercise, quit smoking, etc.)” through a self-report instrument in their questionnaires. Namely, it tries to measure the confidence toward the probability, feasibility, or likelihood of executing given behaviour.

Attitude toward behaviour vs. outcome expectancy

The theory of planned behaviour specifies the nature of relationships between beliefs and attitudes. According to these models, people’s evaluations of, or attitudes toward behaviour are determined by their accessible beliefs about the behaviour, where a belief is defined as the subjective probability that the behaviour will produce a certain outcome. Specifically, the evaluation of each outcome contributes to the attitude in direct proportion to the person’s subjective possibility that the behaviour produces the outcome in question.

Outcome expectancy was originated from the expectancy-value model. It is a variable-linking belief, attitude, opinion and expectation. The theory of planned behaviour’s positive evaluation of self-performance of the particular behaviour is similar to the concept to perceived benefits, which refers to beliefs regarding the effectiveness of the proposed preventive behaviour in reducing the vulnerability to the negative outcomes, whereas their negative evaluation of self-performance is similar to perceived barriers, which refers to evaluation of potential negative consequences that might result from the enactment of the espoused health behaviour.

Social influence

The concept of social influence has been assessed by the social norm and normative belief in both the theory of reasoned action and theory of planned behaviour. Individuals’ elaborative thoughts on subjective norms are perceptions on whether they are expected by their friends, family and the society to perform the recommended behaviour. Social influence is measured by evaluation of various social groups. For example, in the case of smoking:

• Subjective norms from the peer group include thoughts such as, “Most of my friends smoke,” or “I feel ashamed of smoking in front of a group of friends who don’t smoke”;
• Subjective norms from the family include thoughts such as, “All of my family smokes, and it seems natural to start smoking,” or “My parents were really mad at me when I started smoking”; and
• Subjective norms from society or culture include thoughts such as, “Everyone is against smoking,” and “We just assume everyone is a nonsmoker.”

While most models are conceptualized within individual cognitive space, the theory of planned behaviour considers social influence such as social norm and normative belief, based on collectivistic culture-related variables. Given that an individual’s behaviour (e.g., health-related decision-making such as diet, condom use, quitting smoking and drinking, etc.) might very well be located in and dependent on the social networks and organization (e.g., peer group, family, school and workplace), social influence has been a welcomed addition.