13.3: Theory of Planned Behavior

The Theory of Planned Behavior (TPB) was built by Icek Ajzen on a prior theory (Theory of Reasoned Action, first proposed by Martin Fishbein and Ajzen), which describes how an individual might intend to make a behavioral change. This intention is essentially the decision made by the person to “do the thing” right before they do it - intention immediately precedes the behavior. The TPB model involves 3 factors that influence intention: behavioral beliefs, subjective norms, and perceived behavioral control. Behavioral beliefs are those ideas that we hold internally about the behavior; like whether or not it is effective at giving us the desired outcome (McKenzie et al., 2017). As a hypothetical example, if someone believes that exercise is an effective way to improve their health, they are more likely to start a fitness program. Conversely, if they believe that exercise is ineffective, too hard, takes too much time, not worth the effort etc., they probably won’t. These beliefs may be founded in scientific evidence, personal experience, or something else entirely, but they are highly influential on someone's readiness to change a behavior.

The second component of the TPB is the subjective norms of that person’s social circle. These social norms may influence the beliefs that the person has about the behavior, and vice versa (McKenzie et al., 2017). These social norms can also be “positive peer pressure” to engage in healthy behaviors. Using our previous example, if most of a person’s family and friend circle are regular exercisers or involved in sports, they will think of physical activity as the “norm”. Evidence suggests that children and teens are far more physically active when parents are supportive. This support might include role modeling an active lifestyle, taking them to sporting practices and games, verbally encouraging them, or even just active play (Su et al., 2022).

Lastly, in order for a person to change a behavior they need to have “perceived behavioral control”. That is, they need to have the belief that they can change that behavior, they have what it takes. This may include actual behavioral control - meaning the skills, resources, and environment needed to change the behavior - but even if the actual control is there, if the person doesn’t believe they have control over their behavior they are not likely to change it (McKenzie et al., 2017). This concept is very similar to self-efficacy, presented in other models of behavioral change (below). If our hypothetical person believes that exercise improves health, and those around them exercise also, but they don’t believe they’ll ever be able to stick with a fitness program themselves, this alone may prevent them from exercising. See Fig. \(\PageIndex{1}\) for a diagram of the TPB.

Figure \(\PageIndex{1}\): Diagram of the Theory of Planned Behavior.

The TPB has been successfully utilized in several experimental and quasi-experimental studies aiming to improve nutrition, increase physical activity, change traffic safety behaviors (like seat belt wearing in cars or helmet wearing while riding a bicycle), increase safe-sex behaviors, reduce alcohol and drug use, and even improve behaviors at work (like ergonomics and stress reduction). Practitioners can use techniques like providing information, persuasion, skill development, planning, social encouragement, goal setting, motivation, self-monitoring, modeling, and others to help people change their behavioral, normative, and control beliefs - thus increasing their intention to change. Some strategies work better to help a person increase their motivation, which leads to intention. Other strategies might work better after the person has expressed an intention to change; they have the motivation already and now just need the tools (actual control) to reach their goals (Steinmetz et al., 2016).